What is formula of speed?

Answer 1

The definition of speed: speed = distance / time. You can also write this as distance = speed x time. This is used to do various calculations related to speed.

The above is actually only valid for a constant speed. If the speed changes over time, speed - or more precisely velocity - is defined (using derivatives) as v = ds/dt. However, you need to have basic notions of calculus to work with this.