Respuesta :

choixongdong
x + 3y = –9
3x – 3y = 21
-------------------add
4x = 12
  x = 3

substitute x = 3 into x + 3y = –9 
3 + 3y = –9 
3y = -12
  y = -4

Answer
(3, -4) is the solution of the system.

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