The volume of a rectangular box is (x3 - 7x2 - 9x + 63) cubic units. determine the dimensions of the rectangular box by factoring the volume expression completely.

Hello,
well done.
As x^3-7x²-9x+63=(x-3)(x+3)(x-7) we must have x>3 and x>-3 and x>7 thus x>7

Explanations:
x^3-7x²-9x+63=x^3-9x+(-7x²+63)=x(x²-9)-7(x²-9)=(x²-9)(x-7)=(x+3)(x-3)(x-7)