{9x-y/7+2y=3 {12x+5y/3-3x=3
{9x-y=21+6y⇒9x-7y=21/*5⇒45x-35y=105 {12x+5y=9-9x⇒21x+5y=9/*7⇒147x+35y=63 прибавим 192x=168 x=7/8 9*7/8-7y=21 7y=63/8-21 7y=-105/8 y=-105/56