Complete the problem

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters

Solve each quadratic equation by factoring and using the zero product property. x^2 - 8x + 30 = 3x