18
its a number
Remembering BODMAS (Brackets, Orders, Division, Multiplication, Addition, Subtraction), we know that 9+9x9-467 will work out as 9+(9x9)-467 because multiplication comes before addition or...
If you mean 999, that's the UK version of dialing 911. Otherwise, the string has no operators and could just as easily be a 4-digit lottery number.
If you add it all up, the answer is 72.