$(6$ points$)$ Consider the mass spectrometer shown schematically in the figure below. The electric field between the plates of the velocity selector is $5000\frac{V}{m},$ and the magnetic fields in both the velocity selector and the deflection chamber have magnitudes of $0\mathrm{.}050$ T $.$ Calculate the radius $r$ of the path for a doubly charged ion with mass $m=3\mathrm{.}00{10}^{-26}kg.$