The value of a car is related to the amount of time that has passed since its purchase day, and usually the relationship is nearly linear. Suppose that 2 years after being purchased, a car has a value of $17,500, and that 6.5 years after being purchased, the car has a value of $12,100.

(a) Find a linear equation that models the cost C of the car as a function of the number of years x since its purchase day.

(b) Find the slope of the line given by this function, and describe its meaning in words.