Pls help me with this Physics Problems.. Average Speed..?

1) An airplane takes off at 9:00 am and flies at 300 km/hr until 1:00 pm. At 1 pm, its speed is increased to 400 km/hr, and it maintains this speed until it lands at 3:30 pm. What is the airplane's average speed for the entire flight? 2) A car travels at 100 km/hr for 2h, at 60 km/hr for the next 2 hr and... show more 1) An airplane takes off at 9:00 am and flies at 300 km/hr until 1:00 pm. At 1 pm, its speed is increased to 400 km/hr, and it maintains this speed until it lands at 3:30 pm. What is the airplane's average speed for the entire flight?

2) A car travels at 100 km/hr for 2h, at 60 km/hr for the next 2 hr and finally at 80 m/s for 1 hr. Find its average speed for the entire 5h.

3) A man drives one-third of the distance home at 25 mi/hr. How fast must he drive the rest of the way in order to average 35 mi/hr for the entire trip?

Thank you very much to those who'll be helping me.. -.-
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