So you are trying to find the fourth common denominator of 2. So think of the multiples of 2 (2,4,6,8,10) in this place, it is called least common multiple. But if it is put into fraction form, it is 1/2, 1/4, 1/6, 1/8, 1/10. But least common denominator and least common multiple are the same thing. So the least common denominator is 8.