Question

5x + y =21 x - y = 3

Answer 1

$\left \{ {5x+y=21} \atop {x-y=3}} \right.$  +
____________
6x=24
x=$\frac{24}{6}$
x=4

x-y=3
4-y=3
-y=3-4
-y=-1 (-1)
y=1