Let β be the true volume-expansion coefficient of the liquid, A the linear coefficient of copper, and let B be the linear coefficient of silver. Then the vessel's volume-expansion coefficients are 3A (copper) and 3B (silver), and the apparent expansions are C=β−3A,‌‌S=β−3B. Eliminating β,
β=C+3A=S+3B⟹3B=C+3A−S⟹B=‌
C+3A−S
3
So the linear coefficient of expansion of silver is ‌