Three containers $C_1,C_2$ and $C_3$ have water at different temperatures. The table below shows the final temperature $T$ when different amounts of water (given in liters) are taken from each container and mixed (assume no loss of heat during the process)

$C_1$	$C_2$	$C_3$	$T$
$1l$	$2l$	$--$	${60}^{\mathrm{o}}\mathrm{}\mathrm{C}$
$--$	$1l$	$2l$	${30}^{\mathrm{o}}\mathrm{}\mathrm{C}$
$2l$	$--$	$1l$	${60}^{\mathrm{o}}\mathrm{}\mathrm{C}$
$1l$	$1l$	$1l$	$\theta$

The value of $\theta$ (in ${}^{\mathrm{o}}\mathrm{C}$ to the nearest integer) is___________