Question

As per previous question graph motion is not uniform so how v can calculate speed?

Answer 1

The motion need not to be uniform to determine speed. This is because the speed is the ratio between distance travelled and time. The motion can be irregular in between the time.
For example a bus travels with irregular speed in between two points. The distance between two point is 500 metre and time taken for the travel is 200 sec.
So the speed of the vehicle is distanace/time = 500m/ 200 sec= 2.5 m/sec. It never depends on whether the motion is regular or irregular and it depends on the two points only.