The displacement (in meters) of a particle moving in a straight line is given by $$s = 4 t^3 + 2 t - 13,$$ where $t$ is measured in seconds.

Find the velocity of the particle at the times given.

Velocity at time $t=1$ :

Velocity at time $t=2$ :

Velocity at time $t=3$ :

Velocity at time $t=a$ :