"A Cavendish Quantum Mechanics Primer" Excercise 3.7.

I am awfully sorry, but I have rather confused myself about the method for this question and have made myself entirely stuck. Would anyone be able to supply me with the answer such that I may try to find the method to obtain it? Below is linked the question.

https://isaacphysics.org/questions/qmp_ch3_q7?board=qmp_ch3_5_11_2020_r1&stage=university

Nevermind, I have managed to determine the answer; I have attached it below for anyone else as stuck in confusion or their own making as I.

Answer.

(edited 1 month ago)