You can put this solution on YOUR website! The geometric figure you have given is a rectangular parallelipied or a rectangular prism.
Given that a rectangular prism is x units wide, y units long and z units high, then the volume of the prism is V=x*y*z
Back to your problem,
GIVEN: a 6x8x12 prism.
SOLUTION:
volume=(6*8*12)(ft3)
=(48*12)(ft3)
=576 ft3