Answer: V = -2[m/s]
Explanation:
VA= velocity of passenger A, = 1.5 [km/h], it is the same velocity of the side walk
VB= 2+1.5=3.5 [km/h], that is the velocity observed by a person outside of the sidewalk
from the perspective of passenger B the speed of passenger A is VA-VB=-2[m/s]
it means that passenger B is seen how passenger A is getting closer and eventually passing him