Let the relations $R_1$ and $R_2$ on the set $X={1,2,3,\ldots,20}$ be given by $R_1={(x,y):,2x-3y=2}$ and $R_2={(x,y):,-5x+4y=0}$. If $M$ and $N$ are the minimum numbers of ordered pairs that must be added to $R_1$ and $R_2$, respectively, to make them symmetric, then $M+N$ equals: