If you find the volume of each figure separately then add them together, then you'd get your answer.
The formula for volume is V=Base Area*Height, V=BH
So the volume of the smaller cube is 210.
This is because the base area is 15*14. Multiply this by the height, 16, then you get 210.
The volume of the second cube is 25,100. This is because 15+16 is 31. 31*27*30 is 25,100.
If you add both of these volumes together, you're final answer is 25,310 units cubed.
Hope this helped :)