如图电路图所示,电源电压不变,$R_{1}=6\Omega$,$R_{2}=12\Omega$.当$S_{1}$闭合、$S_{2}$断开时,电流表的示数为$1A$；当开关$S_{1}$、$S_{2}$断开时,电流表的示数为$0.2A$.则$R_{3}$的阻值是______$\Omega$,当$S_{1}$、$S_{2}$都闭合时,电流表的示数是______$A$.