how can i find the charge to mass ratio of an electron with the magnetic field value given?

this graph is provided as well

Dear student 

The Determination of the Charge to Mass Ratio of the Electron. A magnetic field produced by Helmholz coils is used to deflect electrons into circular paths whose radii are known. By knowing the energy of the electrons and the magnetic field strength, the ratio of the charge to mass (e/m) of the electron is determined.
The calculated (e/m) ratio is  1.7588196×10^11Ckg ^−1
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