The monthly cost of driving a car depends on the number of miles driven. Lynn found that in May it cost her $460 to drive 500 mi, and in June it cost her $514 to drive 680 mi. (a) Express the monthly cost C as a function of the distance driven d, assuming that a linear relationship provides a suitable model. C(d) = 0.25d+320 (b) Use part (a) to predict the cost (in dollars) of driving 1,600 miles per month.