Answer:
13.5 m
Explanation:
M = Mass of cart = 500 kg
m = Ann's mass = 50 kg
= Velocity of Ann relative to cart = 5 m/s
= Velocity of Cart relative to Ann
As the linear momentum of the system is conserved

Time taken to reach the right end by Ann

Distance the cart will move in the 3 seconds

The negative sign indicates opposite direction
Movement of Ann will be the sum of the distances

The net movement of Ann is 13.5 m