posted by kellie .
Find the resultant force on (a) the mass m1 = 0.183 kg and (b) the mass m2 = 0.106 kg (the masses are isolated from the earth)..
The first mass is 400kg and its 10 cm from the second mass which is 0.183 kg (m1). the second mass is 10 cm away from the third mass which is 0.106 kg (m2).
Not enough info. You need to specify the directions of the masses from each other. The answer is very different if they're in a straight line, as opposed to at the vertices of an arbitrary triangle.
In any case, recall that F = GmM/r^2
Those are the magnitudes of the vectors. You just need to point them in the right direction and add them up.