I've done this so many times

Question

An employee of the cable company made a linear equation of the data using the 2002 cost as a starting value and the 2005 cost as a second data point. What is the company’s equation? Use C for the cost per month and t for time in years since 2002.

Answer 1

C = (Cost2005 - Cost2002)/36 <--- 3 years is 36 months

the linear function is f(t) = Ct + C2002