Question 456599
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How do I substitute a problem like this?
y = x + 3
y = 2x + 12
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In his post, @mananth obtained the solution  x = -9,  y = -6.


This is correct.


But then, @mananth points that the ordered solution is (-6,-9).


This is NOT an ordinary/commonly accepted order.


The ordinary/commonly accepted order is  opposite (x,y) = (-9,-6).