Buses from two different bus routes each stop at the same corner at 9 A. M. Buses from one route stop at that corner every 9 minutes. Buses from the other route stop there every 12 minutes. What is the fewest number of minutes that will pass until the next time buses from both routes are at that corner at the same time? a
21 minutes
b
36 minutes
c
54 minutes
d
108 minutes