Solve for X

4 is right.

I don't know what on earth you did with #1, but here's some basic hints for it:

5x(75x+32y)=5xy
375x^2+160xy-5xy=0
x(375x+155y)=0

So it's a second-degree equation, and one x has to equal 0, but see if you can figure out what the other one equals.