Let the relations $R_1$ and $R_2$ on the set
X={1,2,3,…,20} be given by
$R_1$={(x,y):2x-3y=2} and
$R_2$={(x,y):-5x+4y=0}. If M and N be the minimum number of elements required to be added in $R_1$ and $R_2$, respectively, in order to make the relations symmetric, then M+N equals _____.
