The question is asking for the cubic feet inside the prism, which means it wants the volume.
The volume equation is:
Volume= length x width x height
The issue is: the measurements of the prism are given to us in inches, while the problem asks for feet. We just need to convert each measurement, by dividing each by 12, since there are 12 inches per foot.
40 inches/12=3.33 feet
45 inches/12=3.75 feet
30 inches/12=2.5 feet
Now, we just have to plug in the numbers we found to solve for the volume.
V=(3.33 feet)(3.75 feet)(2.5 feet)
V=31.22 cubic feet