How 9 9 9 can be equals 6?

its a number

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.

A sequence of numbers with any symbols between them are generally taken to represent decimal representations. In this case, it would be 999999 or 1 less than a million.

81.