Answer:
C. x = 3, y = -6
Step-by-step explanation:
You can divide the second equation by 2. Then you have ...
x +2y = -9
This gives you a couple of choices for solution. The x-coefficients match, so subtracting one equation from the other eliminates x:
(x +2y) -(x -2y) = (-9) -(15)
4y = -24 ⇒ y = -6
Adding the two equations eliminates y:
(x -2y) +(x +2y) = (15) +(-9)
2x = 6 ⇒ x = 3
The solution is (x, y) = (3, -6).
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Additional comment
I find it quick and easy to use a graphing calculator to find the solution. Many graphing calculators also make it simple to solve systems of equations in matrix form. Either way, you can obtain a solution in little more than the time it takes to enter the equations (or their coefficients).
