Answer:
D. 4km/min
Step-by-step explanation:
Since the question deals with "speed" and not "velocity", the direction does not matter.
the plane covers 40 + 20 km=60km in 10mins +5 mins=15mins
60 km - 15 mins
1min- 60รท15= 4 mins
therefore, your answer is D. 4km/min