Calculate the wavelength after it undergoes transition

Question

Calculate the wavelength, in nanometers ,of the spectral line produced when an electron in a hydrogen atom undergoes the transition from the energy level n=7 to the level n=2

Answer 1

∆E = R_H (1/n_f² - 1/n_i²)

∆E = change in energy = ?

R_H = -2.179x10^-18 J

n_f = final energy level = 2

n_i = initial energy level = 7

∆E = -2.179x10^-18 J (1/4 - 1/49) = -2.179x10^-18 J (0.2296)

∆E = - 5.00x10^-19 J (negative value since falling from high energy to low energy level)