Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: if a ( a - 9 ) = 10 and b ( b - 9 ) = 10 , where a ≠ b , then a + b =
9
a + b = 19.