Answer:
Juan's Plan
y = .25x+12.95
where y is cost and x is minutes
Tiffany's Plan
y = .15x+14.95
where y is cost and x is minutes
...
Set the cost equal and find where x is the same for both.
.25x+12.95 = .15x+14.95
Group x variables to one side of the equation
.25x + 12.95 - 12.95 - .15x = .15x - .15x + 14.95 - 12.95
.25x - .15x = 14.95 - 12.95
.1x = 2
x=20 minutes
