Electrodynamics: Finding the Potential Using Method of Images

From Griffiths chapter 3 Find the electric potential due to a charge above a flat conductor. What is the charge density on the plate and what is the total charge? Yes, my final answer is off by a factor of 2 - I'm sure it was just a silly mistake. Here is the playlist for the full course https://www.youtube.com/playlist?list=PLWFlMBumSLSYDQww1iwZXEyNJb6xnoxZL