the v-t plot of a moving object is shown in the figure. the average velocity of the object during the first 10 seconds is

Chandni. You forgot to post the plot.

Anyways i give you general idea.

Average velocity = Total distance covered in 10 seconds divided by 10 seconds

Now total distance covered = Area under v-t graph 

You can divide the area into triangular and rectangular sections. Once you get the total distance, divide it by time. Here Total area = 40 + 80 + 20  = 140 m

Average velocity = 140 / 10  = 14 m/s