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)) ∈((A × B) ×(A × B)): a_1+b_2. divides.a_2+b_1}…

Let $\displaystyle \mathrm{A}=\{1,4,7\}$ and $\displaystyle \mathrm{B}=\{2,3,8\}$. Then the number of elements, in the relation $\displaystyle R=\left\{\left(\left(a_1, b_1\right),\left(a_2, b_2\right)\right) \in((A \times B) \times(A \times B)): a_1+b_2\right.$ divides $\displaystyle \left.a_2+b_1\right\}$ is $\displaystyle \_\_\_\_$.