Question 465005
2x-6y=7
3x-9y=10
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6x-18y=21
6x-18y=20
21=20
The way these equations are set up, they are mutually incompatible and unsoluble.  They give two different answers for the same equation..
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The way you did it:
2x-6y=7
2x=7+6y
x=7+6y/2
3(7+6y/2)-9y=10
(21+18y/2)-9y=10
21+18y-18y=20
21=20
Same answer..