The minimum number of elements that must be added to the relation $R=\left\{(a,b),(b,c),(b,d)\right\}$ on the set $\{a,b,c,d\}$  so that it is equivalence relation

$\begin{array}{l}R=\left\{(a,b)(b,c)(b,d)\right\}on\{a,b,c,d\}\\ Rmustbe\{(a,a)(b,b)(c,c)(d,d)(a,b)(b,a)(b,c)(c,b)(b,d)(d,b)\\ (a,c)(a,d)(c,d)(d,c)(c,a)(d,q)\}\\ 13orderpairsshouldbeadded\end{array}$