A question on eqivalence relation

Question

Please explain what the examiner means by asking: Also find [3,6] in Q 1 (a)(i)??

Answer 1

Here $[3,6]$ means the class of $[3,6]$ under the equivalence relation. $$[3,6] = \{(a,b) \in A \times A \mid (a,b)\sim (3,6) \} = \{(a,b) \in A \times A \mid a+6 = b+3 \}.$$

Meaning you have to find all pairs of numbers $(a,b)$ between $1$ and $9$ satisfying $a+6=b+3$. For example, for $a = 1$ we get $b = 4$. If $a = 2$, you get $b = 5$, you get the idea.