The formula of a rectangular prism is V = lwh, or volume = length times width times height.
If the length is 4 inches, width is 5 inches, and height is 7 inches, then you would just do 4 • 5 • 7 to get the volume.
4 • 5 = 20
20 • 7 = 140
So the volume of this rectangular prism is 140 inches^3.
