SPEED

Suppose a car travels 250km in 5 hours then the car will travel 50 km in 1 hour. We say that the speed of the car is 50 km per hour, written as 50 km/hr by speed, we mean here an average speed.
Thus if a rocket 5 seconds to cover 6km
Then its speed will be 6km/5 second = 1.2km/second

Speed = Distance/Time
Distance=Speed * Time
Time =Distance/Speed

In case, a body covers the unequal distance in equal intervals of time its speed is said to be variable.