How you can use a speedometer and a clock to tell how far you have traveled in a car if the cars odometer is not working?

You can use an equation:

Distance = speed x time

Assuming the car is moving at a constant speed for a certain time, the equation will provide the distance the car has traveled. Take a car that is doing 50 miles per hour for 90 minutes. Note that the speed refers to hours as the unit of time so the time used in the equation must also be in hours.

Distance = 50 miles per hour X 1.5 hours

Distance = 75 miles