The monthly cost in dollars of a long-distance phone plan is a linear function of the total calling time in minutes. The monthly cost for 42 minutes of call is $16.42 and the monthly cost for 88 minutes is $21.48. What is the monthly cost for 64 minutes?
We can assume that the linear equation is
Given C(42)=$16.42 and C(88)=$21.48. So,
A linear equation is used to find the cost of a calling plan.