Official solution
For symmetric \[(b,a),(c,b)\in R\]
For transitive \[(a,c)\in R\]
\[\Rightarrow (c,a)\in R\]
\[\therefore (a,b),(b,a)\in R\]
\[\Rightarrow (a,a)\in R\]
\[(b,c),(c,b)\in R\]
\[\Rightarrow (b,b)\in R,(c,c)\in R\]
7 elements must be added