Answer :

Wenqian
    3x+4y=2
 + 4x-4y=12         add them since 4y and -4y can cancel out
    7x=14              divide each side by 7
      x=2 

3x+4y=2   x=2
3(2)+4y=2        substitute 
  6+4y=2
-6       -6
      4y=-4        divide each side by 4
        y=-1
3x+4y=2
4x-4y=12
Add both
7x=14
X=2
Substitute value of x in first equation
Y=-1

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