Step-by-step explanation:
For the first 5 hours of a trip, a plane averaged 120 kilometers per hour.
Distance traveled in first 5 hours = 5 x 120 = 600 km
Let the remainder time be t hours.
For the remainder of the trip, the plane traveled an average speed of 180 kilometers per hour.
Distance traveled in remaining hours = 180 x t = 180t
Total distance traveled = 600 + 180t
Total time taken = 5 + t
Average speed of entire journey = 170 km/hr
We have
Total distance traveled = Average speed of entire journey x Total time taken
600 + 180t = 170 x (5+t)
600 + 180t = 850 + 170t
10t = 250
t = 25 hours
Total time taken = 5 + 25 = 30 hours
Option D is the correct answer.
