Answer:
2268mm^3
Explanation:
To find the volume of the whole shape, an easier way would be to find the volume of each seperate prism and add them together.
The top/smaller prism has dimensions of 4mm x 3mm x 9mm.
Multiply together and you get (4mm x 3mm) x 9mm = 12mm x 9mm = 108mm
The bottom/bigger prism has the dimensions of 12mm x 9mm x 20mm
Multiply together and you get (12mm x 9mm) x 20mm = 108mm X 20mm = 2160mm
Add 108mm + 2160mm and you get the final volume of 2268mm^3
*Because you're working with volume you always add a ^3 after your measurement (units cubed)