Решение
(x - y + 1)/3 - (x + y - 1)/4 = - 3 умножим на 12
(x - y + 1)/2 + (x + y - 1)/5 = 7 умножим на 10
4x - 4y + 4 - 3x - 3y + 3 = - 36
5x - 5y + 5 + 2x + 2y - 2 = 70
x - 7y = - 29
7x - 3y = 67
x = 7y - 29
7*(7y - 29) - 3y = 67
46y = 270
y = 270/46
y = 135/23
y = 5 (20/23)
x = 7 * (135/23) - 29
x = 945/23 - 29
x = 41 (2/23) - 29
x = 12 (2/23)
Ответ: (12 (2/23) ; 5 (20/23)