Where did you get the 9? Which is 3/9

Step 1: The 9 comes from the total number of possible outcomes when you pick one number from set A and one number from set B.

Set A has 3 numbers: $\{2, 4, 6\}$.
Set B has 3 numbers: $\{1, 3, 5\}$.

When you pick one number from A and one from B, you form a pair. To find the total number of unique pairs you can form, you multiply the number of elements in set A by the number of elements in set B.

Total possible pairs = (number of elements in A) $\times$ (number of elements in B)

$$n(S) = 3 \times 3 = 9$$

These 9 possible pairs are:
$(2,1), (2,3), (2,5)$
$(4,1), (4,3), (4,5)$
$(6,1), (6,3), (6,5)$

The 3 in the numerator of $\frac{3}{9}$ represents the number of these pairs whose sum is at least 8.