A body is floating in a liquid. At two temperatures $t_1^{\circ}C\: and \: t_2^{\circ}C$ of the liquid, fractions $f_1 \: and \: f_2$ of the volumes of the body remain immersed in the liquid. Coefficient of volume expansion of the liquid is

Question

$\begin {array} {1 1} (1)\;\large\frac{f_1-f_2}{f_2t_1-f_1t_2} & \quad (2)\;\large\frac{f_1+f_2}{f_1t_1+f_2t_2} \\ (3)\;\large\frac{f_1+f_2}{f_2t_1+f_1t_2} & \quad (4)\;\large\frac{f_1-f_2}{f_1t_1-f_2t_2} \end {array}$