What is the formula for instant velocity when I have time and distance?

v(t)= (d/dt)x(t)

Explanation:

The instantaneous velocity of an object is the limit of the average velocity as the elapsed time approaches zero, or the derivative of x with respect to t. Like average velocity, instantaneous velocity is a vector with dimension of length per time. The instantaneous velocity at a specific time point  t 0  is the rate of change of the position function, which is the slope of the position function  

x ( t ) at  t 0 .