(a) the gold ball acting on the wooden ball ? (b)the wooden ball acting on the gold ball .

Malissa,

The force of gravity between two objects (with mass m1 and m2, respectively) that are d meters apart is

F = G•m1•m2 / d^2

Where G is the universal gravitational constant (which you should have been provided in your text), but is approximately 6.6738 x 10^-11 [(m^3 kg^-1 s^-2)] or 6.6738 x 10^11 [N(m/kg)^2]. The units in brackets are equivalent, but the second set makes it easier to see that when you plug in units of kg for each mass and units of meters for d that they will cancel out leaving only the units for force, Newtons. So pick one mass for m1, the other for m2 and compute using 1m for d. The only difference between the forces is that the force on each object is pointed towards the other object.