Setting up linear equations for problems dealing with specific gravity.

[Agnostic]

I can not, for the life of me, figure out how to set the following up into a system of equations.

An object composed of x gram-mole of lead (specific gravity 11) and y gram-mole of tin(specific gravity 7) weights 82 gram-moles in air and 77 gram-moles in oil of specific gravity of 1/2. Find x and y.

Finding x and y is simple, if I could figure out the right way to set it up...:(

[lightgrav]

I would start with a statement of mass addition,
and a statement of volume addition.
The buoyant Force (5gram)g = V*(.5gram/cm^3)g
gives you a way to write the total Volume.

[Agnostic]

I still cant get it to come out to the correct answer...

[lightgrav]

"correct answer" might be wrong.
maybe youmade an algebra mistake...
what have you done so far?