Question

ХЕЛП ПЛИССС...........................

Answer 1

$\left \{ {{x+2y=5} \atop {3x+y=20}} \right. \\\\\left \{ {{0.5x+y=2.5} \atop {3x+y=20}} \right. \\\\\left \{ {{y=2.5-0.5x} \atop {y=20-3x}} \right.$

y=2.5-0.5x=20-3x

2.5-0.5x=20-3x

2.5-0.5x+3x=20

2.5+2.5x=20

2.5x=20-2.5

2.5x=17.5

x=7

3*7+y=20 ⇒ y=-1

x+y=7+(-1)=6

Відповідь:6