You need to choose between two telephone plans for local cal

You need to choose between two telephone plans for local calls. Plan A charges $25 per month for unlimited calls. Plan B has a monthly fee of $13 with a charge of $0.06 per local call. How many local telephone calls in a month make Plan A the better deal?

Solution

25>13+.06x
25-13>.06x
12>.06x
12/.06>x
200>x calls per month.
Monthy calls less than 200 makes Plan A a better buy.
Proof:
let x=199
25>13+.06*199
25>13+11.94
25>24.94