One cellular phone carrier charges 26.50 a month plus .15cents a minute. another carrier charges 14.50 a month plus .25 cents a minute. for how many minutes is the cost of the plans the same? show work

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