Counting Relations under Divisibility Condition

Let $A = \{1,4,7\}$ and $B = \{2,3,8\}$. Then the number of elements, in the relation $R = \{ ( ( a_{1}, b_{1}) ..$, $( a_{2}, b_{2}) ) \in ((A \times B) \times (A \times B)): a_{1} + b_{2}$ divides $a_{2} + b_{1} \}$ is ____