I need to know how this craftsman calculated the cut angle for his shelf braces. Please, no trigonometry or Pythagorean theorem, there HAS to be a simple way to determine these cuts! My shelves will be 12" square & the braces will be fashioned from six pieces of 1" X 6" X 16" . Thank you in advance!

I have built a 42 inch by 7 feet 1 inch thick black walnut table for my daughter and son in law's new house. I am in a friz of how to finish it. They want tung oil from seeing my other projects. I don't think tung oil is durable and needs to be repeated on occasion. If I did tung oil can I seal it with polyurethane? Give me any details about it you can.