I think you meant [tex]12x^3 + 8x^2 - 3x - 2[/tex] which is equal to:
(3x+2)(2x+1)(2x-1)
the formula for the volume of a rectangular solid is lengthxwidthxheight
V = (3x+2)(2x+1)(2x-1) = lwh
since,
l = 3x+2
w=2x+1
(3x+2)(2x+1)(2x-1) = (3x+2)(2x+1)H
[tex]H = \frac{(3x+2)(2x+1)(2x-1)}{(3x+2)(2x+1)} [/tex]
H= 2x-1