Amobile phone company offers two monthly calling plans, a and b. under a, every minute costs $ 0.10. under b, the first 100 minutes costs $ 12 and every extra minute costs $ 0.08. what monthly talking time would make b the better choice?

A 1min = $0.10
A 100min = $0.10 x 100 = $10
B 100min = $12
B-A = $2
101th min onwards:
A 1 min = $0.10
B 1 min = $0.08
A-B = $0.02

$2 / $0.02 = 100 min
A 200 min = $0.10 x 200 = $20
B 200 min = $12 + ($0.08 x 100) = $20

A 201 min = $20.10
B 201 min = $20.08

Monthly talking time should be 201 minutes and above for B to be the better choice