In a hydrogen atom, from what energy level must an electron fall to the n=3 level to give a line at 1.28 um (micrometers) in the infrared region?

Answer 1

1/wavelength = R(1/3^2 - 1/n^2)
R is the Rydberg constant = 1.09737E7.
wavelength must be converted to m.
1.28 um = 1.28E-6m