может вот так?
{5y - 8(x - 3y) = 7x - 12,{9x + 3(x - 9y)= 11y + 465у-8х+24у=7х-129х+3х-27у=11у+4615х-29у=1212х-38у=46х=-439/111у=-91/37
может вот так?
{5y - 8(x - 3y) = 7x - 12,
{9x + 3(x - 9y)= 11y + 46
5у-8х+24у=7х-12
9х+3х-27у=11у+46
15х-29у=12
12х-38у=46
х=-439/111
у=-91/37