#### Answer

$2160\ in^3$

#### Work Step by Step

To find the area of the figure, find the area of the larger cube and subtract the area that has been cut away.
$10\ in\times12\ in\times20\ in=2400\ in^3$
$3\ in\times4\ in\times20\ in=240\ in^3$
$2400\ in^3-240\ in^3=2160\ in^3$