$\left \{ {{3(x-y)-y =11} \atop {x-2(x+5y)=-15}} \right.$
<=> $\left \{ {{3x-3y-y =11} \atop {x-2x-10y=-15}} \right.$
<=> $\left \{ {{3x-4y =11} \atop {-x-10y=-15}} \right.$
<=> $\left \{ {{3x-4y =11} \atop {-3x-30y=-45}} \right.$
<=> $\left \{ {{3x-4y =11} \atop {-34y=-34}} \right.$
<=> $\left \{ {{3x-4y =11} \atop {y=1}} \right.$
<=> $\left \{ {{3x-4.1 =11} \atop {y=1}} \right.$
<=> $\left \{ {{x=5} \atop {y=1}} \right.$
