C. 409.98 ftÂł
The formula for the volume of a frustum is ...
... V = (h/3)(Bâ + â(BâBâ) + Bâ)
where Bâ and Bâ are the areas of the bases.
Here, we have ...
... Bâ = (6 ft)(8 ft) = 48 ft²
... Bâ = (14 ft)(18 ft) = 252 ft²
So the volume is ...
... V = (3 ft)/3 Ă (48 ft² + â(48¡252) ft² + 252 ft²) â 409.98 ftÂł