Use the PEMDAS / GEMDAS order of operation rule:
(Parenthesis/Grouping, then Exponent/Power, then Multiplication or Division whichever comes first from left to right, then Addition or Subtraction whichever comes first from left to right.)
N = 9 × 9 + 9
N = (9 × 9) + 9
N = (81) + 9
N = 90
Note: Of course, I don't get the "brainliest" because I did not answer this first, hehehe :-). Though I have to reiterate the rule for multi-operation expression.