Paving stones are 6 inches long × 4 inches wide × 1 inch thick. How many paving stones will be required to pave a rectangular space which is 2 feet × 3 feet?

A: <25

B: 25 to 30

C: 31 to 35

D: 36 to 40

E: >40

(I know the answer is D but I don't understand the how to get it)