The apparent coefficient of expansion of a liquid, when heated in a copper vessel is '$\mathit{c}$' and when heated in a silver vessel is '$\mathit{s}$'. If '$\mathit{A}$' is the linear coefficient of expansion of copper then linear coefficient of expansion of silver is :

$\begin {array} {1 1} (a)\;\frac{c+s-3A}{3} & \quad (b)\;\frac{c+3A-s}{3} \\ (c)\;\frac{s+3A-3}{3} & \quad (d)\;\frac{c+s+3A}{3} \end {array}$

$(b)\;\large\frac{c+3A-s}{3}$