it is a circle graph.

I am not sure about the circle graph, but I can show you how to find the common denominator. I assume that the listed numbers are the denominators of your fractions.

The factors of each number are:

3: 3

4: 2 X 2

6: 2 X 3

8: 2 X 2 X 2

Since 8 has three twos as factors, and no other number has more, the common denominator will have three twos. Since 3 and 6 each have 3 as a factor, the least common denominator is going to be:

2 X 2 X 2 X 3 = 24