Board Thread:Questions and Answers/@comment-26177040-20170204031557/@comment-24577221-20170204173812

I'm pretty sure that I know why I made that goof. There's part of my mind that sees "39" as "3 &times; 13", and I more or less automatically substituted 13 for 15 when I was thinking about "what's left over after I subtract the number of hours in a day".