-3х+7у=29
6х+5у=13
2*(-3х)+2*7у=2*29
6х+5у=13
-6х+14у=58
6х+5у=13
-6х+6х+14у+5у=58+13
19у=71
у=71/19
6х+5 * 71/19=13
6х+355/19=13
6х=13-355/19
6х=19*13/19 - 355/19
6х= 247/19-355/19
6х=-108/19
х=-108/19 : 6
х=-108/19 * 1/6
х=-108*1/19*6
х=-108/114
х=-18*6/19*6
х=-18/19
Проверка
-3 * (-18/19)+7 * 71/19=54/19+ 497/19 = 551/19 = 29
6* (-18/19) + 5 * 71/19 = -108/19+ 355/19 = 247/19=13