Question

Can wr prove speed=distance/time mathematically? Or it can be proved with an experiment only?

Answer 1

This is the DEFINITION of speed, in terms of fundamental units.
You can prove someone that the current time is 6 PM by pointing at a clock. But you don't need to PROVE the position of hands because each position has already been assigned a time.
Similarly, you can prove that the speed of a body is x m/s. But you don't need to prove speed itself as it has already been defined as a ratio of distance and time.