What was the energy level of the individual electron of hydrogen atom ( Η )?

[tiffgraf]

Homework Statement

When a excited atom hydrogen ( wavelength ) de-energized emits energy and the electron returns to the fundamental situation. If the wavelength of the radiation emitted is 121 nm, to find what was the energy level of the individual electron of hydrogen atom ( Η ) in the excited state of it.

Homework Equations

I don't know how to solve this so please help me

The Attempt at a Solution

Please help me understand better this chemistry problem and his solution if you want be analytic to the solution
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[Borek]

What is realationship between photon wavelength and energy?