Elimination algebra help?

Question

I was absent yesterday I can figure these two problems out. But I have the final answers just need to figure out how to get them

8. -x -6y = -18
   -x +3y = 9
I did subtraction on the x's cancel out each other so it became -9y = -9 so y would be -1 but on the answer sheet it says y is 0, the if i continued doing the work ignoring y =0 x would be a fraction and my teacher isn't giving us fractions yet. 
Answer: (0, 3)

12. 20x +2y = -6
    -10x -5y = -25
I have know idea how to start this one all i know is it is multiplying and the answer is (-1, 7)

Matt · Accepted Answer

8. -x -6y = -18
-x +3y = 9
ok subtract the second equation
-9y = (-18 - 9)
-9y = -27
y = 3
-x - 6(3) = -18
-x - 18 = -18
-x = 0
x = 0
(0, 3)

12. 20x +2y = -6
2(-10x -5y = -25)
multiply the second equation by 2 so you can eliminate x
20x + 2y = -6
-20x - 10y = -50
add the equations
-8y = -56
y = 7
20x + 2(7) = -6
20x = -20
x = -1
(-1 , 7)

Elimination algebra help?

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