Question

{10(х+у)=30+8х
{9(х-у)=-49-8у

Answer 1

{10(х+у)=30+8х
{9(х-у)=-49-8у

10х+10у=30+8х
9х-9у=-49-8у

2х+10у=30 
9х-у=-49        I 10

2x+10y=30
90x-10y=-490
сложим
92х=-460
х=-5
у=9х+49=-45+49=4
(-5;4)