Velocity is a vector quantity, and speed is a scalar quantity. The speed of a car is 20 m/s. What other information do you need in order to know the velocity of the car ?

Direction

Explanation:

Speed is a scalar quantity, that is, it has only magnitude

While velocity is a vector quantity, which has both direction and magnitude.

Velocity is also called speed with direction.

Hence, we need to know the direction in which the car is moving in order to know the velocity.

unable to answer the rest since your question is incomplete

d.7.5cm is your answer