Question

X+2y=11
X+y=7
METODO SUBSTITUIÇAO

Answer 1

X + 2y = 11
X + y = 7
x = 7 - y
7 - y + 2y = 11
y = 4 

Answer 2

x+y=7
x=7-y

x+2y=11
7-y+2y=11
y=11-7
y=4

x+4=7
x=7-4
x=3