"9 and 9?" Did you possibly mean {2, 5, 6, 9}?
The least common multiple of a set of numbers is the smallest integer that can be divided evenly by all of the numbers. In this case, when I saw the 9 and 5, I thought, "45!" but 45 is not evenly divisible by 2 or 6.
So, I tried 90. 90 is indeed divisible by {2, 5, 6, 9}, and is thus the LCM.
Look up and review "Least common multiple."
