Outside volume
$V_{outside} = 80(40)(12)$
$V_{outside} = 38\,400 \, \text{ ft}^3$
Inside volume
$V_{inside} = 76(36)(12)$
$V_{inside} = 32\,832 \, \text{ ft}^3$
Required volume
$V = V_{outside} - V_{inside}$
$V = 38\,400 - 32\,832$
$V = 5568 \, \text{ ft}^3$
$V = 5568 \, \text{ ft}^3 \left( \dfrac{1 \, \text{ yd}}{3 \, \text{ ft}} \right)^3$
$V = 206.22 \, \text{ yd}^3$ answer