They are the infinitely many multiples of 990.
Common multiples of 9 and 10 are all of the multiples of 90.
I presume you mean what are all the multiples of 9 up to 100 (and not what are all the multiples of 9, 10, 11, ..., 100 of which there are infinitely many): 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99.
90 and all of its multiples.
99 and all its multiples...
That's the same as asking for all the multiples of 360, which is an infinite list.
The common multiples of 9 and 11 are 99, 198, 297 and so on.
Each common multiple of 9 and 10 occurs exactly once (in the list of common multiples), so there is no common multiple that occurs the most. All common multiples of 9 and 10 are the multiples of their least common multiple which is 90.
Multiples of 90.
90 that is all
Just 90.
Multiples of 90
The LCM of 9 and 10 is 90. Other multiples include 180, 270 and 360.