First, find the volume of the whole thing, and then we will remove the cube's volume.
First, the rectangular prism:
V=lwh
V=10(9)(8)
V=720ftcubed
Now, the cube's volume:
V=lwh
V= 3(3)(3)
B= 27ftcubed
Now take our rectangular prism's volume and subtract the cube's
720-27=693ft cubed
So answer choice D is your answer
I hope this Helps!