Crystal bought b boxes of cookies to bring to a party. Each box contains 18 cookies. She decides to keep two boxes for herself. She brings 90 cookies to the party. Which equation can be used to find the number of b boxes Crystal bought?
A) 2b − 18 = 90
B) 18b − 2 = 90
C) 18b − 36 = 90
D) 36 − 18b = 90