The answer is “147 cubic meters”
The volume of a rectangular prism = length • width • height
If you plug in the numbers from the figure, you then get your equation:
V = 5 • 3 • 8
V = 120 cubic meters
The volume of a cube = a^3, where a equals a side measure.
If you plug in the numbers from the figure, you get your second equation:
V = 3^3 OR 3 • 3 • 3
V = 27 cubic meters
Now you add up both volumes to get your total volume of the whole composite solid:
120 + 27 = 147 cubic meters
I hope this helped! Good luck!