Answer
$A(w)=w^{2}+10w$, $w\gt 0$
Work Step by Step
We are told that the poster has length 10 inches longer than the width ($l=w+10$). Therefore, the area is:
Area=length*width=$l*w=(w+10)w=w^2+10w$
We should restrict $w\gt 0$, since the width can't be negative.
