What i'm going to do is give you the questions as well as the answers. i need you with understanding the reasons behind their answers. no matter what i do i cant seem to get what they've gotten as answers.

part a: how much energy does the electron have initially in the n=4 excited state?
−1.36×10^−19

part b: what is the change in energy if the electron from part a now drops to the ground state?
−2.05×10^−18

part c: what is the wavelength lambda of the photon that has been released in part b?
9.72×10^−8