A car travels uphill at 30 km/hr and downhill at 90 km/hr. It goes 100 km uphill and 50 km downhill. Find the average speed of the car?  Choose the correct choice from the following.
A) 32 kmph
B) 39 kmph
C) 34 kmph
D) 35 kmph
E) 36 kmph

Rationale: "avg speed = total distance / total time . total distance traveled = 100 + 50 = 150 km ; time taken for uphill journey = 100 / 30 = 10 / 3 ; time taken for down hill journey = 50 / 90 = 5 / 9 ; avg speed = 150 / ( 10 / 3 + 5 / 9 ) = 39 kmph answer : b"
Answer: B