-g+F/A=h^3 for A

-g+F/A=h^3 for A

Add g to each side:
-g + g+F/A=h^3 + g

Cancel the g's on the left side:
F/A = h^3 + g

Cross multiply:
F = A(h^3 + g)

Divide each side by (h^3 + g)
F/(h^3 + g) = A(h^3 + g)/(h^3 + g)

Cancel (h^3 + g) on the right side:
A = F/(h^3 + g)