Show total number of Comments

Howdy again! I’ve gotten myself into a real mind boggle with this issue. I’m trying to display the total number of comments for each (not by each) authors posts. For instance if an author has 4 post and 12 comments on each post that would be 48 total comments. I would like that number to be displayed but I just can’t figure out how to go about it because the data is in two different tables. It’s probably pretty simple and I”m making it complicated but I’ve spent 9 hours on queries and php and nothing has worked out. So I’m asking for a little bump in the right direction.

As always-Thanks in Advance