length, width, and height are (b+2), (b-2), (b+3)
Explanation:
Doing what the problem statement tells you to do, you get ...
(b^3 +3b^2) -(4b +12)
= b^2(b +3) -4(b +3) . . factor each pair of terms
= (b^2 -4)(b +3) . . . . write as a product
= (b -2)(b +2)(b +3) . . . . use the factoring of the difference of squares
The three factors are (b-2), (b+2), and (b+3). We have no clue as to how to associate those with length, width, and height. We just know these are the dimensions of the box.