Let the number of minutes be = x.
Cost per minute = 11 cents = 0.11
Phone Bill = Monthly fee + 0.11* x
Substituting from the question
20.82 = 3 + 0.11x
3 + 0.11x = 20.82
0.11x = 20.82 - 3
0.11x = 17.82
x = 17.82/0.11
x = 162
Lamar was billed for 162 minutes.