Car A travels west from an intersection at a constant speed of 60 mi/h, passing the intersection at 1:00 P.M. Car B travels north from the same intersection at a constant speed of 45 mi/h, passing the intersection at 1:30 P.M. How fast is the distance between the two cars changing at 2:00 P.M.?
a) 84 mi/h
b) 61.5 mi/h
c) 72 mi/h
d) 75 mi/h