Mathematics - Sets and Relations Question with Solution | TestHub

Let $A=\{2,3,6,7\}$ and $B=\{4,5,6,8\}$. Let $R$ be a relation defined on $A\times B$ by $\left(a_1,b_1\right)R\left(a_2,b_2\right)$ if and only if $a_1+a_2=b_1+b_2$. Then the number of elements in $R$ is _________