Question 391221
x+3y=1..........................1 
-3x-3y=-15
/3
-x-y=-5.........................2
add (1) & (2)
x-x+3y-y=+1-5
2y=-4
/2
y=-2
...
plug value of y in (1)
x+3*(-2)=1
x-6=1
add 6
x=7
...
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