What is retardation? What is its direction?

The acceleration-time graph for a particle is given in the figure. If it starts motion at $t=0$, the distance travelled in $3 \, s$ will be ........... $m$.

$A$ particle is moving in a straight line such that its velocity is increasing at $5\,m/s$ per meter. The acceleration of the particle is .......... $m/s^2$ at a point where its velocity is $20\,m/s$.

$Assertion$ : Retardation is directly opposite to the velocity.
$Reason$ : Retardation is equal to the time rate of decrease of speed.

$A$ particle starts from rest. Its acceleration $(a)$ versus time $(t)$ graph is as shown in the figure. The maximum speed of the particle will be.....$m/s$.

An object with a mass $10 \, kg$ moves at a constant velocity of $10 \, m/s$. $A$ constant force then acts for $4 \, s$ on the object and gives it a speed of $2 \, m/s$ in the opposite direction. The acceleration produced in it is ........ $m/s^2$.