Could someone please help me with this physics question?

[rjdfhorn]

The masses and coordinates of three spheres are as follows: 16 kg, x = 1.50 m, y = 2.25 m; 42 kg, x = -1.50 m, y = -3.75 m; 56 kg, x = 0.00 m, y= -0.50 m. What is the magnitude of the gravitational force on a 12 kg sphere located at the origin due to the other spheres?