on # 4 I think I'm some what heading in the right direction but I get stuck half way through

I drew the cube and I know that on the base l=w which I set equal to x, then I know that the volume equals l*w*h or in this case V=x^2 h and since v=100 you can solve for h which is 100/x^2. So then I created another equation for the perimeter which i set equal to 4x+4(2x+2h) and then i substituted h from the first equation into the second equation. Then I solved for x but I didn't come very close to the actual answer so I don't really know where I went wrong.

6.1 part 2 #4