Factor completely:

40x^5y^2 - 32x^7y^6 + 28x^8y^4 - 36x^7y^5

I thought factor completely meant solve for the unknown variable. However, I have no idea what the answer is for this question. I know the greatest common denominator is 4x^5y^2. But do not know how to get on further. What do I do?

14. A rectangular field is to be enclosed on four sides and divided by another section of fence parallel tot he width using 4800m of fencing. What is the maximum area of the entire field? What are the dimensions of the field that maximums the area?

How would I even start this? I know that A = l x w. But other than that I have no idea. I thought it would be something like x (4800 -x) and then solve for x, but I don't think that will give me the correct answer. How do I do this question?