We aim to determine silver's linear expansion coefficient, given a liquid's apparent expansion in copper and silver containers.
A liquid's apparent expansion, when heated within a container, is affected by both the liquid and container's expansion. The apparent coefficient of expansion, \( C \) (copper) and \( S \) (silver), reflects both the liquid's and the container's expansion.
The formula for apparent expansion in a vessel is:
\[
\beta_{\text{apparent}} = \beta_{\text{liquid}} + \beta_{\text{vessel}}
\]
Where:
- \( \beta_{\text{apparent}} \) is the liquid's apparent expansion coefficient.
- \( \beta_{\text{liquid}} \) is the liquid's expansion coefficient.
- \( \beta_{\text{vessel}} \) is the vessel material's expansion coefficient.
Step 1: Apparent Expansion Coefficients in Copper and Silver
- In a copper vessel:
\[
C = A + \beta_{\text{liquid}}
\]
where \( A \) is copper's linear expansion coefficient, and \( \beta_{\text{liquid}} \) is the liquid's expansion coefficient.
- In a silver vessel:
\[
S = B + \beta_{\text{liquid}}
\]
where \( B \) is silver's linear expansion coefficient.
Step 2: Solving for Silver's Expansion Coefficient
We have the following 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 simplifies to:
\[
B = S - C + A
\]
Therefore, silver's linear expansion coefficient is:
\[
\boxed{ \frac{C + 3A - S}{3} }
\]
Consequently, the correct answer is:
\[
\boxed{(B) \frac{C + 3A - S}{3}}
\]