Simplify.
Complex Fractions.
b-2b/b+3/1/b+3+1/b-3=
LCM: (b+3)(b-3)
Try typing in your expression at wolframalpha.com
and keep adding parentheses until it interprets your text correctly!
I suspect you mean
b - 2b/(b+3)
-----------------
1/(b+3) + 1/(b-3)
If not, maybe you can clear things up a bit. Online text formatting requires a bit more effort.