Electric Field linearly accelerates $e^{-}$ from voltage in Electron Gun: Va
200 V

$\Rightarrow v_0= $ ${8.386\cdot 10^6}$ $\frac{\text m}{\text s}$

Magnetic Field circularly accelerates $e^{-}$ from current in Helmholtz coils through coils: Iα
1.75 A

$\Rightarrow B=$ ${1.31\cdot 10^{-3}}$ $\text {T}$

Schematic Diagram

Schematic layout of the experiment about electron deflection in a magnetic field
Picture of the real experiment for deflection of electrons in a magnetic field
Grid for data logging
$r =\,$$\,\rm{cm}$

Measure the radius of the electron trajectory in the experiment and type your solution in the red framed plot line.
With help of the plot you can check your solution.