Equation for $30 for the first 500 minutes for a cell phone plus $.20 for each additional minutes. ?

Question

Equation for $30 for the first 500 minutes for a cell phone plus $.20 for each additional minutes. ?

Answer 1

Divide 500 (minutes) by 30 (dollars) and you get 16.666666666666666666666666666667 which is your cent per minute cost for regular use.  

Answer 2

(minutes used - 500) * $.20 + $30 = amount owed

But it wouldn't work if you used less than 500 minutes

Answer 3

30x + 20=500