Let $A = \{2, 3, 4\}$ and $B = \{8, 9, 12\}$. Then the number of elements in the relation $R = \{ ( ( a _ { 1 } , b _ { 1 } ) , ( a _ { 2 } , b _ { 2 } ) ) \in ( A \times B ) \times ( A \times B ) : a _ { 1 }$ divides $b _ { 2 }$ and $a _ { 2 }$ divides $b _ { 1 } \}$ is\\
(1) 36\\
(2) 24\\
(3) 18\\
(4) 12