12^3 is 1728.
times pie, 3.1415 is 5428.5
times 4/3 is 7238 inches cubed
I rounded a bit so it may not be exact, but it works just as it's written, no tricks except to raise the radius to the 3rd first.
edit: I see you got it, but another way I liked to write it was [4*pie*(r^3)]/3