Rani goes to school from home at a certain speed and returns to home at the speed of 50 km/h. If the distance between her home and school is 20 km and the average speed of the whole journey is 37.5 km/h, then what is her speed from home to school?

A

45 km/h

B

30 km/h

C

35 km/h

D

40 km/h