how do i calculate the wavelength of light emitted by a hydrogen atom?

Answer 1

Do you know the shells involved in the electron movement. If so, then
E = 3.18 x 10^18 J [(1/n₁²) - (1/n₂²)]

Answer 2

typo.
That 3.18 x 10^18 should be
2.18 x 10^-18
The answer is in units of Joules/photon. That is for one transition of one electron.