On the left, the name should be: multiples of 3 because each are a multiple of 3 like 3, 6, 9, 12 from 3x1 is 3, 3x2 is 6, and so on. The right one should be named multiples of 5, because like the multiples of 3 but now 5, all are multiples of 5 like 5x1 is 5, 5x2 is 10 and so on. The middle is multiples they have in common/share.