The volume of a rectangular solid is
V = l • w • h
Volume equals length times width times height
length = 12
width = x
height = x - 1
volume = 504. Therefore
504 = 12 (x)(x - 1) divide by 12
42 = x(x - 1) or 42 = x^2 - x
x^2 - x - 42 = 0 or (x -7)(x + 6) = 0
x = 7 and/or. X = -6. Negative not posible
x = 7 for width, x - 1 = 6 for the height
and 12 is the length