Первая система:
(x - y)/2 - (x + y)/4 = -3
y/2 - (x+y)/5 = 0
2x - 2y - x - y = -12
5y - 2y - 2x = 0
2x - 6y = -24
3y - 2x = 0
-3y = -24 ------- y = 8
24 - 2x = 0 -------- x = 12
Ответ: x = 12 ; y = 8
Вторая система:
(x + 2y)/10 - (x + 4y)/3 = -8
(2x - 3y)/2 - (x + y)/6 = 0
3x + 6y - 10x - 40y = -240
6x - 9y - x - y = 0
7x + 34y = 240
5x - 10y = 0
35x + 170y = 1200
35x - 70y = 0
240y = 1200 --------- y = 5
35x = 350 ------------ x = 10
Ответ: x = 10 ; y = 5.