V=lwh they give me a rectangle with 3 sides. one side is 3x-1 another is x+2 and the last one is 2x+1. they...

V=lwh

they give me a rectangle with 3 sides.

one side is 3x-1 another is x+2 and the last one is 2x+1.

they also already give me the answer which is 6x^3+13x^2+x-2.

I know how to get the 6x^3 but I need to know the rest.