Question 662051
Plan A:  18.50
Plan B:  6.50 + .1(x)
where x is minutes after 40 minutes
18.50 < 6.50 + .1x
18.50 < 6.50 = .1x
12 < .1x
x > 120
The plans are equal when x in plan B is 120, which means the user has used 120 minues above the alloted 40 minutes.
So A < B when x > 120