A cellular phone company offers several different services plans. One option, for people who plan on using the phone only in emergencies, costs the user $5.05 per month plus $0.60 per minute for each minute the phone is used.
a. Write a linear function for the monthly cost of the phone in terms of a number of minutes the phone is used.
b. Use your equation to find the cost of using the cellular phone for 18 minutes in 1 month.