Mass spectrometer, some please help with this equation!

Question

ok, i have posted a couple of these wierd magnetic equations i can't understand. my book is of no help because it's written for ..well..physics people! can someone please help explain this in lamen terms to help me solve??

An ion (charge = -e) enters a mass spectrometer.

The speed of the ion is 2.50×106 m/s; the magnetic field is B = 2.06 T; the diameter of the circular path is 0.379 m. Determine the mass of the ion.

Answer 1

Centripetal aceleration: mv^2/r

Put this equal to the electromagnetic force on the moving charge, and solve for m.