I used to love math. But over the years the educators have been changing the "rules" of mathematics. No wonder our children are confused. Old math, new math, and back to old math again.
Have you solved the problem above? I personally refer to this as one understood. -(-36) is like -1*-36=36
So -19-17=-36+36=0-12=-12. Have I lost you yet? When I first looked at the problem I was lost. I had to walk away and come back to it before I could solve it.