Another way of presenting this question is to ask: what is the volume of the prism. Sometimes, you can get tripped up on the terminology and fail to discover what it is the question is really asking. To find the volume of this concave prism, we can divide it into two boxes: top box and bottom box. Imagine slicing a knife through the line where the two "steps" intersect. From there, we can apply the basic formula for a rectangular prism and add up the volumes.
Top Box:
A = height x length x width
A = 10 x 40 x 20
(the height is 10 because it is equal to the tallest height minus the shorter height)
A = 8000 in. cubed
Bottom Box:
A = height x length x width
A = 20 x 60 x 20
A = 24000 in. cubed
Total Volume = 24000 in. cubed + 8000 in. cubed = 32000 in. cubed
Hoped this helped!
