Acceleration of a particle moving in a straight line is expressed by

$\frac{d^2 s}{dt^2} = 2t$

where, $s$ denotes distance (m) and $t$, time (s). At time $t = 0$, the distance and velocity of the particle are 0 m and 3 m/s respectively. The distance travelled by the particle in m after 3 s is