Question 861778
{{{x^2+y^2+136=4(5y-3x)}}}
{{{x^2+y^2+136=20y-12x}}}
{{{x^2+12x+y^2-20y=-136}}}
{{{(x^2+12x+36)+(y^2-20y+100)=-136+36+100}}}
{{{(x+6)^2+(y-10)^2=0}}}
{{{(y-10)^2=-(x+6)^2}}}
{{{y-10=0 +- sqrt(-(x+6)^2)}}}
{{{y=-10 +- sqrt(-(x+6)^2)}}}
So then,
{{{x+y=x-10 +- sqrt(-(x+6)^2)}}}