The easiest way to probably do this is to go through the times table of seven in your head and find anything similar numbers in the 6's multiplication table.
6: 6,12,18,24,30,36,42,
7: 7,14,21,28,35,42
42 is the first number that comes in both of the tables. Therefore the least common multiple of seven and six is 42.
30
12
12
Is 12.
90
42
168
The LCM is: 210
The LCM is: 54
The LCM is 630.
One, you freakin' idiot.
420
LCM(6, 7, 9) = 126.
168 is the least common multiple of 56 and 84
30
30
12