Question

Kevin purchased a prepaid phone card for $30.00. Calls cost 9 cents a minute using this card. The credit, C (in dollars), left on the card after it is used for x

minutes of calls is given by the following function.
C(x) =30.00 – 0.09x
How much credit is left on the card after Kevin uses it for 20 minutes of calls?

Answer 1

If trying to solve for x it would be x = 30 over C+0.09. If trying to solve for C then it would be C=30 over x - 0.09.