I need math help, its pre-calculus by the way!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!?

[~$^*:DaMaN:*^$~]

Ok, here is the question:
A pulley having a 9-inch diameter is belted to a pulley having a 6-inch diameter. If the large pulley runs at 120 rpm (revolutions per minute), how fast does the small pulley run?

A) 80 rpm
B) 100 rpm
C) 160 rpm
D) 180 rpm
E) 240 rpm

pleases show your work, as best as possible, and give the answer

i really appreciate it, thank you!