GCF
factor them and find the group of factors common to both
example
18 and 24
18=2*3*3
24=2*2*2*3
common group is 2*3 or 6
gcf=6
LCM=least common multiupule
means smallest number that both can go into evenly
factor them and make a group that includes both of them, if you have repeats, replace them
18 and 24
18=2*3*3
24=2*2*2*3
LCM=2*2*2*3*3=72