A rectangular sheet of cardboard measuring 24cm by 18cm has squares of side xcm cut from each corner. The sides are then folded up to form an open box. Which one of the following polynomials represents the volume V(x) (in cubic centimetres) of the box?
a) 4x3+84x2−432x
b) 4x3−84x2+432x
c) x3−42x2+432x
d) 4x3−96x2+432x