The annual cost of owning and operating a car, C dollars, is a linear function of the distance

The annual cost of owning and operating a car, C dollars, is a linear function of the distance, d kilometers, it is driven.

c = md + b

The cost is $4600 for 10 000 km and $9100 for 25 000 km. 

(a) Determine the values of m and b.

(b) Write c as a function of d.