Answer:

Step-by-step explanation:
The total volume will simply be the sum of each storage space.
We can see that the storage space on the right as a total volume of 12 cubic feet.
The storage space on the left will have a volume of:

(This is the volume formula for a cube).
Therefore, the <em>total</em> storage space will be:

Our answer is the bottom-right choice.
And we're done!