A motel clerk counts his $1 and $10 bills at the end of a day. He finds that he has a total of 60 bills having a combined monetary value of $186. What is the system of equations that can be used to find the number of $1 bills, x, and the number of $10 bills, y, that he has?
A: x=y=60
x+10y=186
B: x+y=60
10x+y=186
C: x+y+186
10x+y=60
D: x+y=186
x+10y=60
