Answer:
r = 0.11 m
Step-by-step explanation:
Let's suppose that the magnetic field is perpendicular to the vector speed. In that case, the centripetal force would be the same as the Lorentz force.

.
Solving this equation for r, we will have:

Now, to find r we need to get the speed of the particle. Let's use the law of conservation of energy. The kinetic energy is equal to the electric potential energy:
, but

So we would have:
, then

Finally
Have a nice day!