Answer:
3 m /s
Step-by-step explanation:
Average velocity is defined as the ratio of total displacement to the total time taken. The formula of average velocity is given by

Take east direction is positive and west is negative.
Here the total displacement is
d = 20 - 40 + 35 = 15 m
t = 5 second
Average velocity = 15 / 5 = 3 m/s