2x + 4 = 9 - y

Answer 1

y= -2x-13
x= 5.5 -1/2y

Answer 2

2x + 4 = 9 - y,
y + 2x + 4 = 9,
y + 2x = 9 - 4,
y + 2x = 5,
y = 5 - 2x.

2x + 4 = 9 - y,
2x = 9 - y - 4,
2x = 5 - y,
x = 5/2 - y/2.