Figure ahead represents the displacement-time sketch of motion of two cars A and B. Find the velocity of car A.

Here, the displacement-time graph of car A is a straight line which shows that the velocity of the car remains a constant.
We know, the slope of displacement-time graph represents velocity.
Velocity of car A= Slope of line A
$=V_a=\frac{\Delta Y}{\Delta X}=\frac{80\text{km}-0\text{km}}{2\text{h}-0\text{h}}=40{\text{kmh}}^{-1}$
Velocity of car A is $40{\text{kmh}}^{-1}$.