Hi Chad Q.,
The area (A) of a rectangle is equal to its length (L) times its width (W).
The equation is A = L*W.
In your problem you are given the length equal to 16 inches so L=16.
You are also given the area equal to (32x + 48) so A=(32x + 48).
Lets plug them into the equation A = L*W.
(32x + 48) = 16*W
Divide both sides by 16 and you end up with:
(32x + 48)/16 = W, this is the equation for the width.
I hope this helps, Joe.