Question 141018
2x-y=10 multiply this equation by 3 & add them.
6x-3y=30
x+3y=-9 
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7x=21
x=21/7
x=3 answer.
2*3-y=10
6-y=10
-y=10-6
-y=4
y=-4 answer.
proof
3+3*-4=-9
3-12=9
-9=-9