The magnetic force acting on an object of charge q is
[tex]F=qvB \sin \theta[/tex]
where
q is the charge
v is the speed of the object
B is the magnetic field intensity
[tex]\theta[/tex] is the angle between the directions of v and B.
In our problem, the direction of the bullet is perpendicular to the magnetic field, so [tex]\theta=90^{\circ}[/tex] and [tex]\sin \theta=1[/tex], so we can ignore it in the formula.
Therefore, we can use the data of the problem to calculate the magnetic force on the bullet:
[tex]F=qvB=(2.0 \cdot 10^{-12}C)(300 m/s)(7.0 \cdot 10^{-5} T)=4.2 \cdot 10^{-14} N[/tex]
