Let X O Z-plane divides the joining the point (2,3,1) and (6,7,1) into m:n, then the co-ordinate of X O Z-plane is(m+nmx2+nx1,m+nmy2+ny1,m+nmz2+nz1)=(m+n6m+2n,m+n7m+3n,m+nm+n)But on the XOZ-plane y-coordinate will be zero, thenm+n7m+3n=0⇒nm=−73∴m:n=−3:7