A car completes a journey in 12 hours at an average speed of 52 km/h.
a) how far did he travel?
b) If the car had travelled 65 km/h for the whole journey, by how much time would the journey have been shortened?
c) If the first half of the journey had been completed at 52km/h, and the second half at 65km/h, find the average speed for the journey.