Question

4x - y = 0
x - y =15

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Answer 1

$\left \{ {{4x-y=0} \atop {x-y=15}} \right.$

$(4x-y)-(x-y)=0-15$

$4x-y-x+y=-15$

$3x=-15$

$x=-\frac{15}{3}$

$x=-5$

$x-y=15$

$-5-y=15$

$-y=15+5$

$-y=20$

$y=-20$