Hi
Letting x, (x-1)(x+9) represent the length, height and width respectively
Question states***
x(x-1)(x+9)= 72 in^3
solving for x
x^3 + 8x^2 - 9x - 72 = 0 |x = 3 is one solution found by substitution
(x-3)(x^2 + 11x + 24)= 0 |dividing (x^3 + 8x^2 - 9x - 72) by (x-3)
factoring the quadratic
(x-3)(x+3)(x+8) = 0 |tossing negative solutions out for length
x = 3
Dimensions of the box are 3in long, 2in high, 12in wide