3 because if you add 7+8 it equals 15 and if you add 2+1 it = 3 so they are both divides by 3
3*7 = 21
21 and 5
21
10.5 x 2=21
21 and 7
21 x 3
3 and 7
79
The LCM (least common multiple) is 21. So the LCM in this case is the same as the two numbers multiplied.
-43
21
It can't be done with whole numbers....but if you want decimals....these two will work 3.7731879764631448414184572689148 17.226812023536855158581542731085