finding magnitude of gravitational force?

[gadawg90]

The masses and coordinates of three spheres are as follows: 16 kg, x = 0.75 m, y = 3.00 m; 34 kg, x = -2.50 m, y = -2.75 m; 60 kg, x = 0.00 m, y= -0.75 m. What is the magnitude of the gravitational force on a 30 kg sphere located at the origin due to the other spheres?

2. Relevant equations
i know to use this equation:F=(GMm)/r^2


i know you have to do a^2+b^2=c^2 to find the radius of each sphere but i just dont know what to do after that...

[mgb_phys]

The 'r' in the equation is the distance between the (centres) of the sphere it's not their radius

(we use 'r' in the law because it's usually the radius of an orbit 0

[gadawg90]

alright well if i find r then what do i do next?

[mgb_phys]

Find 'F' for each object, then the overall direction/magnitude of F ( a diagram might help)

[gadawg90]

im still confused. when i find the distance what do i use as the second mass in the equation. and when i find F for all three spheres how do i find the gravitational force for the sphere at the origin?