A car is moving along x-axis . As shown in figure, it moves from O to P in 18 seconds and return from P to Q in 6 seconds. What is the average velocity and average speed of the car in going from

a)O to P
b)From O to P and back to Q

a) O to P
it moves from OQ to QP therefore, the distance is equal to OQ +PQ 
average velocity = displacement/ time taken
in this case, displacement is equal to the distance and it should be divided by time taken 

Average speed =distance/time taken

b) O to P and back to Q
average velocity=displacement /time taken 
=OP-PQ/ total time taken=18+6=24 seconds
average speed= distance/total time taken
= OQ+QP/24 seconds