Gravitational Force of Three Identical Masses

[PSEYE]

Homework Statement

Three identical masses of 550 each are placed on the x axis. One mass is at X1= -10.0 , one is at the origin, and one is at X2= 43.0 .
What is the magnitude of the net gravitational force on the mass at the origin due to the other two masses?

G = 6.673 x 10-11

Homework Equations

I'm using just the regular force of grav.

F_grav= GMm/R^2

Net force:
F_net= F1-F2

and I tried Gm^2(1/X1^2-1/X2^2)

I'm getting logical numbers, but they're not right.

I calculated Force1 to be -0.00202
I calculated Force2 to be 0.00109

I think I may have squared the mass to get the these numbers...what do I do with the masses? there are three of them, do I use 1650? or 550?

 

[PSEYE]

got it