Question 199244
To do this, you need the formula for volume of a rectangular prism.

V of rect prism = length * width* height = (a-3)

We know the length = (a-3)/(a-7) and the height, or depth = (a+b)/(a-7)

Therefore we can solve for the width:

 a-3 =  (a-3)/(a-7) * (a+b)/(a-7) * width

That is the conceptual part of the problem. With a little algebra, you can solve for the width in terms of a. (You will not get an exact answer)