Please show me the step on how to do this. I know the answer but how do you get it.

A rectangular garden with a 4-feet wide cement sidewalk is shown. The cement for the sidewalk is 1 foot deep.

What volume of cement is needed for the sidewalk?

A) 96 cubic feet
B) 120 cubic feet
C) 192 cubic feet
D) 240 cubic feet

Please show me the step on how to do this I know the answer but how do you get it A rectangular garden with a 4feet wide cement sidewalk is shown The cement for class=