The volume of a box is (width)(length)(height).
V = W*L*H
Plug in all the information we have:
84 ft^3 (incorrectly written as ft sq in the question)
84 ft^3 = (x)(x+1)(x-4) = (x)(x^2-3x-4) = x^3 - 3x^2 - 4x.
Next, think of the factors of 84. 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, and 84.
The value is x = 6.
(6)(6+1)(6-4) = (6)(7)(2) = 84
