Reddit mentions of Numerical Methods for Engineers, Sixth Edition

All of the books I can see from top to bottom on Amazon:

1. http://www.amazon.com/Elements-Chemical-Reaction-Engineering-Edition/dp/0130473944 -- used price: $90.98.
   
2. http://www.amazon.com/Molecular-Thermodynamics-Donald-McQuarrie/dp/189138905X/ref=sr_1_1?s=books&ie=UTF8&qid=1407531821&sr=1-1&keywords=molecular+thermodynamics -- used price: $70.00 (paperback is $29.99)
   
3. http://www.amazon.com/Physical-Chemistry-Molecular-Donald-McQuarrie/dp/0935702997/ref=sr_1_1?s=books&ie=UTF8&qid=1407531925&sr=1-1&keywords=physical+chemistry+a+molecular+approach -- used price: $72.44 (paperback is $42.65)
   
4. http://www.amazon.com/Quantum-Physics-Molecules-Solids-Particles/dp/047187373X/ref=sr_1_1?s=books&ie=UTF8&qid=1407532022&sr=1-1&keywords=quantum+physics+of+atoms+molecules+solids+nuclei+and+particles -- used price: $52.66
   
5. http://www.amazon.com/Introduction-Chemical-Engineering-Thermodynamics-Mcgraw-Hill/dp/0073104450/ref=sr_1_1?s=books&ie=UTF8&qid=1407532094&sr=1-1&keywords=introduction+to+chemical+engineering+thermodynamics -- used price: $129.96 (paperback is $84.38)
   
6. http://www.amazon.com/Organic-Chemistry-8th-Eighth-BYMcMurry/dp/B004TSKJVE/ref=sr_1_5?s=books&ie=UTF8&qid=1407532227&sr=1-5&keywords=organic+chemistry+mcmurry+8th+edition -- used price: $169.33 (paperback is $79.86)
   
7. http://www.amazon.com/Elementary-Differential-Equations-William-Boyce/dp/047003940X/ref=sr_1_7?ie=UTF8&qid=1407532549&sr=8-7&keywords=Elementary+Differential+Equations+and+Boundary+Value+Problems%2C+9th+Edition+solutions -- used price: $8.00
   
8. http://www.amazon.com/Numerical-Methods-Engineers-Sixth-Edition/dp/0073401064/ref=sr_1_1?ie=UTF8&qid=1407532859&sr=8-1&keywords=numerical+methods+for+engineers+6th+edition -- used price: $47.99 (paperback is $22.48)
   
9. http://www.amazon.com/Applied-Partial-Differential-Equations-Mathematics/dp/0486419762/ref=sr_1_5?s=books&ie=UTF8&qid=1407532927&sr=1-5&keywords=applied+partial+differential+equations -- used price: $8.32 (paperback is $1.96)
   
10. http://www.amazon.com/Transport-Phenomena-2nd-Byron-Bird/dp/0471410772/ref=sr_1_1?s=books&ie=UTF8&qid=1407533036&sr=1-1&keywords=transport+phenomena+bird+stewart+lightfoot+2nd+edition -- used price: $28.00
    
11. http://www.amazon.com/Basic-Engineering-Data-Collection-Analysis/dp/053436957X/ref=sr_1_2?s=books&ie=UTF8&qid=1407533106&sr=1-2&keywords=data+collection+and+analysis -- used price: $80.00
    
12. http://www.amazon.com/Calculus-9th-Dale-Varberg/dp/0131429248/ref=sr_1_1?s=books&ie=UTF8&qid=1407533219&sr=1-1&keywords=calculus+varberg+purcell+rigdon+9th+edition+pearson -- used price: $11.97 (paperback is $2.94)
    
13. http://www.amazon.com/Elementary-Principles-Chemical-Processes-Integrated/dp/0471720631/ref=sr_1_1?s=books&ie=UTF8&qid=1407533286&sr=1-1&keywords=elementary+principles+of+chemical+processes -- used price: $161.72
    
14. http://www.amazon.com/Inorganic-Chemistry-4th-Gary-Miessler/dp/0136128661/ref=sr_1_1?s=books&ie=UTF8&qid=1407533412&sr=1-1&keywords=inorganic+chemistry+messler -- used price: $75.00
    
15. http://www.amazon.com/Fundamentals-Heat-Transfer-Theodore-Bergman/dp/0470501979/ref=sr_1_1?s=books&ie=UTF8&qid=1407533484&sr=1-1&keywords=fundamental+of+heat+and+mass+transfer -- used price: $154.99 (loose leaf is $118.23)
    
16. http://www.amazon.com/Biochemistry-Course-John-L-Tymoczko/dp/1429283602/ref=sr_1_1?s=books&ie=UTF8&qid=1407533588&sr=1-1&keywords=biochemistry+a+short+course -- used price: $139.00 (loose leaf is $115)
    
17. http://www.amazon.com/Separation-Process-Principles-Biochemical-Operations/dp/0470481838 -- used price: $93.50 (international edition is $49.80)
    
18. http://www.amazon.com/University-Physics-Modern-13th/dp/0321696867/ref=sr_1_1?s=books&ie=UTF8&qid=1407545099&sr=1-1&keywords=university+physics+young+and+freedman -- used price: $83.00
    
    Books & Speakers | Price (New)
    ---|---
    Elements of Chemical Reaction Engineering (4th Edition) | $122.84
    Molecular Thermodynamics | $80.17
    Physical Chemistry: A Molecular Approach | $89.59
    Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles | $128.32
    Introduction to Chemical Engineering Thermodynamics (The Mcgraw-Hill Chemical Engineering Series) | $226.58
    Organic Chemistry 8th Edition | $186.00
    Elementary Differential Equations | $217.67
    Numerical Methods for Engineers, Sixth Edition | $200.67
    Applied Partial Differential Equations | $20.46
    Transport Phenomena, 2nd Edition | $85.00
    Basic Engineering Data Collection and Analysis | $239.49
    Calculus (9th Edition) | $146.36
    Elementary Principles of Chemical Processes, 3rd Edition | $206.11
    Inorganic Chemistry (4th Edition) | $100.00
    Fundamentals of Heat and Mass Transfer | $197.11
    Biochemistry: A Short Course, 2nd Edition | $161.45
    Separation Process Principles: Chemical and Biochemical Operations | $156.71
    University Physics with Modern Physics (13th Edition) | $217.58
    Speakers | $50.00
    
    Most you can get is $1476.86 (selling all of the books (used and hard cover) in person), and if you sell it on Amazon, they take around 15% in fees, so you'll still get $1255.33. But wait...if you sell it to your university's book store, best they can do is $.01.
    
    Total cost: $2832.11 (including speakers)
    
    Net loss: -$1355.25 (books only). If sold on Amazon, net loss: -$1576.78 (books only). Speakers look nice; I wouldn't sell them.
    
    Edit: Added the two books and the table. /u/The_King_of_Pants gave the price of speakers. ¡Muchas gracias para el oro! Reminder: Never buy your books at the bookstore.
    
    Edit 2: Here are most of the books on Library Genesis
    Thanks to /u/WhereToGoTomorrow

Your question is extremely broad but I would suggest this textbook as a starting point. We used it in school for some optimization problems.

https://www.amazon.com/Numerical-Methods-Engineers-Steven-Chapra/dp/0073401064

However, it is worth noting that the "optimum" solution for a structural engineering problem is not always as simple as solving for the least weight solution. Constructability, schedule, architectural considerations, etc play a major role in a succesful project and that doesn't come from iterating properly to a least-cost or least-weight solution.