Time and Distance - General Questions

A car covers 420 km in 3 hours. At what speed must it travel to cover the same distance in 2 hours?

A car travels from A to B at 20 km/hr and returns from B to A at 80 km/hr. What is the average speed for the whole journey?

A car travels from A to B at 20 km/hr and returns from B to A at 30 km/hr. What is the average speed for the whole journey?

Walking at 6/7 of his usual speed, a man is 2 minutes late. What is his usual time to cover the distance?

A car travels from A to B at 15 km/hr and returns from B to A at 30 km/hr. What is the average speed for the whole journey?