PHysics Question? I need help with this one problem.?

Question

I'm a bit stuck on this question.

I got part A but I dont understand B and C

Can someone explain it to me in detail ? Thank you, that would be very helpful!!

You drive on interestate 197 from Bowie to Greenbelt, one half the time at 35 mi/h and the other half at 55 mi/h. on the way back you travel one half the distance at 35 mi/h and the other half at 55 mi/h. what is your average speed (a) from Bowie to Greenbelt. (B) from freenbelt to bowie. and (C) for the entire trip?

The answers are :

a) 45 mi/h which i got

b) 42.8 mi/h

c) 43.9 mi/h

Answer 1

From the information given, all I get is 45 mph

a) Bowie to Greenbelt = 35 / 2 + 55 / 2  = 45 m/h

b) Greenbelt to Bowie = 55 / 2 + 35 / 2 = 45 m/h

c) Round trip = 35 / 4 + 55 / 4 + 55 / 4 + 35 / 4 = 45 m/h