I'm only posting here because I am not seeing any way to do this in my Text book and my two math help books.

I'm stuck on the first one.Let .

Find

and

I'm trying to use the Additive Interval Property as Shown Below.

Where a= 13, b=16.

So I try:

But keep ending up with the wrong answer, I've resorted by trying different combinations but with no success (even substitution).