All sides of a cube are the same.
So to calculate the volume, you only need to know the measure of one side.
The formula for the volume of a cube is the length of the edge to the power of 3.
The measure of the known edge is 9, so the formula for volume would be 9^3.
9^3 is 9 • 9 • 9, which is 9 times 9 times 9.
9 • 9 = 81
81 • 9 = 729
The volume of this cube is 729 cubic feet.
There must be a typo in the answer choices because 729 cubic feet is the answer for the volume of the cube, even though it's not listed.