First off, the formula for volume is :
length x width x height
Or
base x height
Assuming the each unit is 1, there is 2 rows of 3, or 6 units as the base.
There are 5 units up, representing height.
So, you multiply 6 x 5, and get 30.
Therefore, your answer should be C!
I hope this helps!! ~(^v^)~