Multiply r^2+7r+10/3 by 3r-30/r^2-5r-50
(r^2+7r+10/3) * (3r-30/r^2-5r-50)1/3(3r^2+21r+10) x 3(r-10)/(r^2-5r-50)(3r^2+21r+10)x(r-10)/(r^2-10r+5r-50)(3r^2+21r+10)x(r-10)/(r-10)(r+5)3r^2+21r+10/(r+5)
