Question 207417
Find the prime factors for each of the given numbers.
2,3,5 are easy
6 = 2*3
9=3*3
10=2*5
So you can see that the least common multiple will be the one that contains the factors as follows
one 2
two 3 (since 9 is 3*3)
one 5 
Why 2 threes? and not 2 of anything else? Look at the factors for each and pick number of prime factors used 'the most' in any one of the original numbers.
10 can be made using one 2 and one 5. 6 is onw 2 and one 3. Only 9 requires using any of the common factors more than once.

So the number is {{{2*3*3*5 = 90}}}