Answer
$5*10^6 \frac{m}{s}$
Work Step by Step
We get $qvB = \frac{mv^2}{r} = 3.2*10^{-15}$. Since $qvB = 3.2*10^{-15}$, as the force is wholly caused by the magnetic field, $v = \frac{3.2*10^{-15}}{1.6*10^{-19}*0.004}$. Evaluating, we get $5*10^6 \frac{m}{s}$.
