A cellular phone company offers several different service op

A cellular phone company offers several different service options. One option, for people who plan on using the phone only in emergencies, costs the user $4.55/month plus $0. 55/min for each minute the phone is used Write a linear function for the monthly cost y of the phone in terms of the number of minutes x the phone is used. Use the function to find the cost of using the cellular phone for 13 min in 1 month.

Solution

Let x be the number of minutes for which the phone is used in a month, by the people who plan on using the phone only in emergencies and let y be the cost of using the phone in a month. Then the fixed cost of using the phone is $ 4.55 per month. In addition, the variable cost, depending on the phone usage is $ 0.55x. Hence, the required linear function is y = f(x) = 0.55x + 4.55.

The cost of using the phone for 13 minutes in a month is 0.55*13 + 4.55 = 7.15 +4.55 = $ 11.70.