Ответ:
{ 3(a - d) - 12 = a + d
{ 2(a - d) - 14 = a + d
3(a - d)-12 = 2(a - d)-14
3a - 3d - 12 = 2a - 2d - 14
a-d = -2
a=d-2
3(d - 2 - d) - 12 = d - 2 + d
2d = -16
d = -8 a = -10
Проверим: 3(a - d) - 12 = 2(a - d) - 14
3(-10+8) - 12 = 2(-10+8) - 14
3*(-2) - 12 = 2*(-2) - 14
-18 = -18
Ответ: (-10; -8)