Hi I have facing difficulty with solving the 10th part of the Problem 4 in Chapter 3.2

This equation is quite different from others in Problem 4, since I am really not sure with my solution, can anyone check for me? My friend said he will solve it in a different way and he thinks my solution is wrong but he did not actually solve it. I have attached the question and my solution. It is really near the quiz and I have struggled on this problem for two days, please help me!