Since the period of revolution of electrons in a uniform magnetic field rapidly increases with the growth

Question:

Since the period of revolution of electrons in a uniform magnetic field rapidly increases with the growth of energy, a cyclotron is unsuitable for their acceleration. This drawback is rectified in a microtron (Fig. 3.105) in which a change AT in the period of revolution of an electron is made multiple with the period of accelerating field To. How many times has an electron to cross the accelerating gap of a microtron to acquire an energy W = 4.6 MeV if ∆T = To, the magnetic induction is equal to B = 107 mT, and the frequency of accelerating field to v = 3000 MHz?