Help!

A pyramid  on the same base with the same height of its associated prism will have a volume of 1/3 of the prism

But the pyramid here has only 1/2 the base of its associated prism

So....its volume  = (1/3(1/2)12   = 2 units^3

So...the volume of the remaining piece  = 

(12 - 2) units^3  =

10 units^3