Question

{   х+у=7
{
{  5х-7у=11

Answer 1

$left { {{x + y=7 |*7} atop {5x - 7y=11}} right.$
$left { {{7x + 7y=49} atop {5x - 7y=11}} right.$
________
12x = 60
x = 5

$left { {{x=5} atop {y=2}} right.$