What quantity can you calculate if you know that a car travels 30 km inn 20 minutes?

Knowing the distance covered and the time to cover the distance,
you can calculate the car's average speed during that time.

           Average speed = (distance covered) / (time to cover the distance)

           Average speed  =  (30 km) / (20 minutes)  =  1.5 km/minute .

Note:  You do NOT have enough information to calculate velocity.