The electromotive force on the free electrons in the wire is given by
E=vBl
where v is the velocity, B is the field component perpendicular to the wire and l is the length of the wire. So we get
E=15.6*40E-6*2.5m=1.56mV
Now the force that causes this to happen is given by F=q(v X B) where q is the charge on the electron which is negative. the cross product of the velocity and magnetic field points in a direction that is westward. Since the electrons are negative they are pushed to the east, leaving the west end of the wire with a positive charge .
100m so you will subtract 100m from 200m. and you will get your answer 200m-100m=100m
