In a uniform gravitational field:
Calculate the center of gravity for each material.
Calculate the mass (weight) of each material.
The mass of material one will act as if it is all located at cg1.
The mass of material two will act as if it is all located at cg2.
So now it is a teeter totter... (Now look up teeter totter physics on wikipedia.) (The mass of the plank is zero.)
From memory, I think that the distances from the fulcrum times the corresponding mass will be a constant. (more math.)
d1 x mass1 = d2 x mass2.
d1 + d2 = dTotal = distance between cg1 and cg2.
The fulcrum point is the combined center of mass.
- Brian

d1 = D*m2/(m1+m2) (?)

https://www.onlinemathlearning.com/lever-problems.html

It has been very hard to find good references on google :-)

===SeeSaw