AMC 8 2007 Problem 4

A haunted house has six windows. In how many ways can Georgie the Ghost enter the house by one window and leave by a different window? $\mathrm{(A)}\ 12 \mathrm{(B)}\ 15 \mathrm{(C)}\ 18 \mathrm{(D)}\ 30 \mathrm{(E)}\ 36$