9 cubic feet
Explanation
The volume of a cone is given by:
[tex]\text{Volume}_{cone}=\frac{1}{3}base\cdot height[/tex]then
let
[tex]\begin{gathered} \text{base}=9ft^2 \\ \text{altitude}=3\text{ ft} \end{gathered}[/tex]replace in the formula
[tex]\begin{gathered} \text{Volume}_{cone}=\frac{1}{3}base\cdot height \\ \text{Volume}_{cone}=\frac{1}{3}\cdot9ft^2\cdot(3\text{ ft)} \\ \text{Volume}_{cone}=\frac{1}{3}\cdot9ft^2\cdot(3\text{ ft)} \\ \text{Volume}_{cone}=9ft^3 \end{gathered}[/tex]so, the answer is 9 cubic feet
I hope this helps you
