The displacement (in meters) of a particle moving in a straight line is given by the equation of motion $s=4t^3+6t+2$, where $t$ is measured in seconds. Find the velocity of the particle at times:

(a) $t=a$.
(b) $t=1$.
(c) $t=2$.
(d) $t=3$.

(a) $v(a) =$ m/s
(b) $v(1) =$ m/s
(c) $v(2) =$ m/s
(d) $v(3) =$ m/s