We need to find for all combinations of edges
For edge (1,2)
Does vertex 3 comes while traversing from 1 to 2 ? No
so the numerator is 0
The shortest path between 1 to 2 is only 1
so the denominator is 1
= 0/1 = 0
For edge (1,4 )
Does vertex 3 comes while traversing from 1 to 4 ? Yes, it comes once
so the numerator is 1
The shortest path between 1 to 4 is 2 [1-2-4, 1-3-4]
so the denominator is 2
= 1/2 = 0.5
For edge (1,5)
Does edge (3,5) comes while traversing from 1 to 5 ? Yes
so the numerator is 1
The shortest path between 1 to 5 is 1 [1-3-5]
so the denominator is 2
= 1/2 = 0.5
Similarly,
For edge (1,6)
1/3 = 0.33
For edge (2,4)
0/1 =0
For edge (2,5)
1/3 = 0.33
For edge (2,6)
0/1 =0
For edge (4,5)
1/2 = 0.5
For edge (4,6)
0/1 = 0
For edge (5,6 )
0/1 = 0
Finally summing all the values, we get
0.5 + 0.5 + 0.33 + 0.33 + 0.5 = 1.5 + 0.66 = 2.16