A motorist travels a certain distance x in five hours at an average speed of 90km/h.what average speed must she maintain to cover the distance in 4 hours?

Answer 1

distance = speed * time = 5*90 = 450 km/hr
speed = distance/time = 450/4 = 112.5 km/hr

Or, you can reason like this: 4/5 the time means 5/4 the speed. 5/4 * 90 = 112.5