Motion of charged particle in uniform magnetic field

[muffintop]

Homework Statement

Accelerating voltage of 2500V is applied to an electron gun producing a beam of e^- originally traveling horizontally north in a vacuum toward a viewing screen 25cm away. a. What are the magnitude and direction of the deflection caused by Earth's gravitational field? b. What are the magnitude and direction of the deflection on the screen caused by the vertical component of the Earth's magnetic field B=20x10^-6 T
I just need an explanation for b. please

Homework Equations

r= mv/ |q|B

The Attempt at a Solution

v=2.96x10^7 (found from part a)
r=8.44m
sin$$\theta$$=.35/r
deflection=8.44m(1-cos$$\theta$$)