If you cannot get a chair to move across the floor, it is because static friction opposes your push. When you say static or kinetic friction the two object that facing each other are opposing each other. That's why you're having a hard time pushing the chair.
Average speed = Distance traveled / time taken
In this case Time taken = Difference in hours between 3 PM and 9 AM
= 6 hours
Total distance traveled = 350 km + 250 km
= 600 kilometers
So average speed = 600/6 = 100 km/hr
Average speed of bus = 27.78 m/s
So the bus's average speed = 27.78 m/s or 100 km/hr.
