bài 11
$\left \{ {{2x+2y=340} \atop {3x-4y=20}} \right.$ đáp án x=100 và y=70
12
$\left \{ {{x-2y=0} \atop {-5x+5y=-41}} \right.$
13
$\left \{ {{2x+2y=100} \atop {-x+2y=-18}} \right.$
14
$\left \{ {{2x+2y=56} \atop {-2x+4y=24}} \right.$
15
$\left \{ {{2x+2y=124} \atop {3x+5y=435}} \right.$
16
$\left \{ {{5x+4=y} \atop { \frac{x+3}{y+3}=2,5 }} \right.$
17
$\left \{ {{7x-1=y} \atop {\frac{(x+7)4}{y+5}=5 }} \right.$
