(9+11)+1=-1 is this answer
correct?

No, that answer is not correct.

Start with  (9 + 11) = 20  and go from there.

When you learn the "order of operations"  (PEMDAS), you learn
that the ' P ' means 'parentheses' . . . the first thing you're supposed
to do is get rid of them.  If there are only numbers inside, then you
do the inside arithmetic until there's only one number, and then you
can throw away the parentheses.
  
                                                            - (9 + 11) + 1

Add the numbers in the parentheses:  - (20) + 1

Throw away the parentheses:              - 20  +  1

Combine what you see there now:       - 19

Is that equal to  -1 ?
I don't think so.
The equation in the question is not true.
-1  is not the answer .