We are asked to find the linear coefficient of expansion of silver given the apparent coefficient of expansion of a liquid when heated in copper and silver vessels.
The apparent coefficient of expansion of a liquid, when placed in a container, depends on the coefficient of expansion of both the liquid and the container. Specifically, the apparent coefficient of expansion \( C \) of the liquid in a copper vessel and \( S \) in a silver vessel are influenced by both the liquid's expansion and the container's expansion.
The formula for the apparent coefficient of expansion when the liquid is in a vessel with a material having a coefficient of linear expansion is:
\[
\beta_{\text{apparent}} = \beta_{\text{liquid}} + \beta_{\text{vessel}}
\]
Where:
- \( \beta_{\text{apparent}} \) is the apparent coefficient of expansion of the liquid in the vessel,
- \( \beta_{\text{liquid}} \) is the coefficient of expansion of the liquid,
- \( \beta_{\text{vessel}} \) is the coefficient of expansion of the vessel material.
Step 1: Apparent Coefficient of Expansion in Copper and Silver Vessels
- The apparent coefficient of expansion of the liquid in a copper vessel is given by:
\[
C = A + \beta_{\text{liquid}}
\]
where \( A \) is the coefficient of linear expansion of copper, and \( \beta_{\text{liquid}} \) is the coefficient of expansion of the liquid.
- The apparent coefficient of expansion of the liquid in a silver vessel is given by:
\[
S = B + \beta_{\text{liquid}}
\]
where \( B \) is the coefficient of linear expansion of silver.
Step 2: Solving for the Coefficient of Expansion of Silver
We now have the following system of equations:
1. \( C = A + \beta_{\text{liquid}} \)
2. \( S = B + \beta_{\text{liquid}} \)
To find \( B \), subtract the first equation from the second:
\[
S - C = B - A
\]
This gives:
\[
B = S - C + A
\]
Thus, the linear coefficient of expansion of silver is:
\[
\boxed{ \frac{C + 3A - S}{3} }
\]
Therefore, the correct answer is:
\[
\boxed{(B) \frac{C + 3A - S}{3}}
\]