Easy way is to list multipules of 6 6,12,18,24,30,36,42,48,54 so we can see that A doesn't work because 20 doesn't have 6 as a common factor C works D doesn't work because of the 56
answers are B and C
another way is to factor each notice that 6=2*3 so factor each and see if we can find a 2*3 in each
A. 12=2*2*3, so there is a 6 20=2*2*5, not 6
B. 18=2*3*3, so there is a 6 24=2*2*3*3, so there is a 6 works
C. 30=2*3*5, there is a 6 54=2*3*3*3, there is a 6 works
D. 42=2*3*7, there is a 6 56=2*2*2*7, there isn't a 6 nope
