A 30-Kg Mass Is Located at (0

A 3.0-kg mass is located at (0.0 m, 8.0 m) , and a 1.0-kg mass is located at (12 m, 0.0 m) . You want to add a 4.0-kg mass so that the center of mass (or center of gravity) of the three-mass system will
Be at the origin. What should be the coordinates of the 4.0-kg mass?

A) (-12 m, -8.0 m)
B) (-6.0 m, -3.0 m)
C) (3.0 m, 6.0 m)
D) (-3.0 m, -6.0 m)