Why not allow a quick simple answer: 4009?
We don't really say "four thousand nine" in English. We say four thousand and nine. The only exception I can think of is when we are talking about the year, as in "back in two thousand nine"
Maybe they are Americans.
In Australia we would even say "back in two thousand and nine".
correct English is four thousand AND nine
The numberic answer of this question is
4009 is this right