Precalculus (6th Edition) Blitzer

$A= 2x^2+\frac{32000}{x}$
Step 1. Assuming the height is $h$, we have the volume as $V=x^2h=8000$, which gives $h=\frac{8000}{x^2}$ Step 2. The surface area can then be expressed as $A=2x^2+4xh=2x^2+4x(\frac{8000}{x^2})=2x^2+\frac{32000}{x}$