i'm going to use m for minutes
Cell carrier 1
0.15 per minute (0.15m)
$26.50 first, and then add on for every minute
cost carrier 1 = 0.15m + 26.50
carrier 2
0.25 per minute (0.25m)
$14.50 first, and then add on for every minute.
cost carrier 2 = 0.25m + 14.50
to find out when they cost the same, make the two costs equal to each other:
0.15m + 26.50 = 0.25m + 14.50
all that's left is to solve for m
0.15m + 26.50 = 0.25m + 14.50
subtract both sides by 0.15 m
26.50 = 0.2m + 14.50
subtract both sides by 14.50
12 = 0.1 m
divide both sides by 0.1
m = 120
the phone carriers will have the same cost at 120 minutes
