Answer:
C.

Step-by-step explanation:
We must find two volumes, that of the quadrangular prism and that of the pyramid of the top and finally add them to get the total volume.
Quadrangular prism volume:

where
is the base area
and H is the height

Volume of the quadrangular pyramid:

To find the value of height H we use pitagoras:

Thus

The total volume is :

Wich is option C.