Why is instantaneous velocity defined?

For an object moving on a straight line,draw $x-t$ graphs for:
$(i)$ When it is at rest.
$(ii)$ When it is moving with constant velocity in the positive direction.
$(iii)$ When it is moving with constant velocity in the negative direction.
$(iv)$ When it performs non-uniform motion.

$A$ bird flies with a velocity $(t-2) \text{ m/s}$ along a straight line, where $t$ is the time in seconds. The distance covered by it in a time of $4 \text{ s}$ is: (in $\text{ m}$)

Let us define a motion as $A$ when velocity is positive and increasing,$A^{-1}$ when velocity is negative and increasing,$R$ when velocity is positive and decreasing,and $R^{-1}$ when velocity is negative and decreasing. Now,match the following two columns for the given $s-t$ graph.

Column $I$	Column $II$
$(A)$ $M$	$(p)$ $A^{-1}$
$(B)$ $N$	$(q)$ $R^{-1}$
$(C)$ $P$	$(r)$ $A$
$(D)$ $Q$	$(s)$ $R$

Explain instantaneous velocity.

$A$ particle shows a distance-time curve as given in the figure. The maximum instantaneous velocity of the particle is around the point: