Question 346243
Use the common denominator {{{z^2r^2}}}
{{{(z+r)/(zr^2) + (2z+r)/(z^2r) = (z(z+r))/(z^2r^2) + (r(2z+r))/(z^2r^2)}}} 
{{{(z+r)/(zr^2) + (2z+r)/(z^2r) = (z(z+r)+r(2z+r))/(z^2r^2)}}} 
{{{(z+r)/(zr^2) + (2z+r)/(z^2r) = (z^2+rz+2rz+r^2)/(z^2r^2)}}} 
{{{(z+r)/(zr^2) + (2z+r)/(z^2r) = highlight((z^2+3rz+r^2)/(z^2r^2))}}}