Solve by substitution:
x+y=9
y=2x
x+y=9 2x=4 because 2x2=4
y=2x
x+2x=9
x+4=9
-4 -4
x=5
x+y=9
chick answer by 5+4=9
x+y=9
y=2x
y=2x
x+2x=9
x+4=9
-4 -4
x=5
x+y=9
chick answer by 5+4=9