Roger started with 90 items in his MP3 collection. Each month, he buys 15 more MP3s to add to his collection. The number of MP3s in his collection, P, is given by P = 15m + 90, where m is the number of months he has added 15 MP3s to his collection. How many MP3s will be in Roger’s account in 9 months?
A. 90
B. 105
C. 225
D. 315