How do I find the initial energy of an electron given the wavelength and the final energy

hey

An electron jumps to the n = 4 level of a hydrogen atom after absorbing a photon of wavelength 1875 nm.
What energy level did the electron move from?

I haven't found equations for how to to find the energy absourbtion, just emission.

I know that the values are negative when the electron is jumping up to a level, but I don't know how to proceed in terms of what equation to use or how to solve.

Energy absorbed and emitted are same if the energy levels are same .Use same equation and only take care of final state and initial sate of energy levels .

Detla E = -RH [1/ n(f)^2  - 1/n(i)^2]

for absortion this value  is positive.

Calculate E using plancks equation 

E=hc/λ