Answer: (x,y) = (2,7)
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Explanation:
-x = y-9 turns into x = -y+9 when you multiply both sides by -1
Plug this into the first equation y - 2x = 3 to get the following
y - 2x = 3
y - 2( x ) = 3
y - 2(-y+9) = 3 ... replace x with -y+9
y + 2y - 18 = 3
3y - 18 = 3
3y = 3+18
3y = 21
y = 21/3
y = 7
Which then tells us,
x = -y+9
x = -7+9
x = 2
So x = 2 and y = 7 pair up to get the solution (x,y) = (2,7)
