commonly called the elimination method
I would multiply the first by 5
---> -15x + 60y = - 135
multiply the 2nd by 3
---> 15x + 60y = 45
add them:
120y = - 90
y = -90/120 = -3/4
sub that into either of the two originals to get the x
solve this system of equations using the linear combination method
-3x+12y=-27
5x+20y=15
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