electromagnetic radiation of which frequency (in Hz) can be emitted by the hydrogen atom upon transition of an electron from n= 6 to n= 2 according to the bohr model.

What't the question? If you want to know the wavelength it is

1/wavelength = R(1/2^2 - 1/6^2)
R = Rydberg constant = 1.097E7
You can convert to frequency by
c = frequency x wavelength.