LCM of 6 and 18 is ___.

When we find the lowest common multiple, using prime factorisation method, then the LCM will be the product of all prime factors with the highest degree. 

Now, for 6 and 18 the LCM can be found out as follows:

Let us reduce 6 and 18 to its prime Factors.

6 = 2 x 3

18 = 2 x 3 x 3 = 2 x 3²

Considering the highest power of all factors we get:

LCM (6, 18) = 2 x 3² = 18