Two-thirds of a certain distance was covered at the speed of 45 km/h, one-fourth at the speed of 60 km/h and the rest at the speed of 75 km/h. Find the average speed per hour for the whole journey. (correct to 2 decimal places)

A

51.25 km/h

B

45.75 km/h

C

58.25 km/h

D

49.77 km/h