The garage shown is a composite of more than one shape. which of these would be a correct way to find its volume?
a. add the volume of a rectangular prism to the volume of a triangular prism.
b. add the volumes of a rectangular prism and a pyramid
c. find the volume of a pyramid
d. find the volume of a rectangular prism

B - Add the volumes of a rectangular prism and a pyramid

If you look at the diagram, you can see it is a pyramid roof on top of a cuboid room.
The cuboid is a rectangular prism as it has the same cross section throughout its length. The top part however does not and so it is a pyramid not a triangular prism.
Therefore to get the volume of the whole thing, you just add the volumes of the 2 parts together.