Question

metodo da adiçãox+y=10 e x -3y=-18

Answer 1

$\left \{ {{x+y=10~~(-1)} \atop {x-3y=-18}} \right.$

$\left \{ {{-x-y=-10} \atop {x-3y=-18} \right.$

$-4y=-28\\4y=28$

$y= \frac{28}{4}$

$\boxed{y=7}$

$x+y=10\\x=10-y\\x=10-7\\\boxed{x=3}$

Answer 2

x+y=10  (3)
x-3y=-18

3x+3y=30
x-3y=-18

4x=12
x=12/4
x=3

x+y=10
y=10-x
y=10-3
y=7