The y variable has the same coefficient so use elimination (subtract equations).
-2x = 8 - 6y
-(-15x = 21 - 6y)
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13x = -13 + 0
x = -1
Use this to find y in either equation.
-2(-1) = 8 - 6y
2 = 8 - 6y
2 - 8 = -6y
-6 = -6y
y = 1
(x,y) = (-1, 1)
