How to solve the problem--step-by-step:
m=each minute
plan A:
$15+$0.14x
plan B:
$20+$0.09x
Solve
15+0.14x=20+0.09x
15-15+0.14x=20-15+0.09x
0.14x=5+0.09x
0.14x-0.09=5+0.09x-0.09
0.05x=5
0.05x/0.05=5/0.05
x=100
Thus, at 100 minutes, the two plans cost the same.
Check Work
plan a: 15+0.14(100)= $29
plan b: 20+0.09(100)= $29
Solution is correct.