Answer:
Volume of a rectangular prism can be found with the equation
v = length × width × height
They are trying to trip you up a little bit here because they give 2 measurements in feet then the last in inches. So for your prism...
18 inches = 1.5 ft
v = l×w×h
v = 3×2×1.5
v = 9 ft^3
Volume=length*width*height, so first you would have to change the units of the inches to feet, which would be 90/12=7.5, so now you can fit that into the equation, 2*3*7.5=45 ft cubed!