The electron in a hydrogen atom changes energy level from $n=1$ to $n=3.(16)$

a$.$ Does this transition endothermic or exothermic? Explain briefly.

b$.$ Calculate the energy and wavelength of this transition.

c$.$ If the electron transitioned from a $3d$ to a $3p$ orbital, what is $DE?$

d$.$ What is the potential energy of the electron when it is no longer associated with the nucleus?