Three balls with masses of 6 g at (1,9), 1 g at (7,6), and 7 g at (5,1), respectively, are connected by massless rods. The balls are located (in meter intervals) as in the ?gure (coordinates given above with their mass). A horizontal force in the left- to-right direction (1 N) ˆ? is applied to the 6 g ball. What is the acceleration of the center of mass?