All the walls have the same height. Two of the walls will span a distance equal to the length and their areas will be l*h. Two of the walls will span a distance of the width, and their areas with be w*h.
a) Total area = 2(l*h) + 2(w*h) = 2h(l+w)
b) start with A = 2h(l+w). Isolate h, since that is what you want to find.
Get rid of the 2 by dividing each side by 2
Get ride of the (l+w) by dividing each side by (l+w)
c) Use your expression for h found in step b) and substitute the given values in for A, l, and w
d) We need a formula for the area, A. In step b), A = 2h(l+w). If l=w and we want to write the equation for A with only width and height, we get rid of l. Let's rewrite l as w, since l=w.
A = 2h(w+w)
w+w=2w, so A = 2h(2w) = 4hw, so A=4hw