Perpendicular lines have slopes that are recriprocals and opposite signs.
Your equation x + y = - 4
solved for y is... y = - x -4 (this line has a slope of -1)
Your new line needs a slope of +1
y = x + b
Solve for b by plugging in x and y
-6 = 3 + b
- 9 = b ANSWER: y = x - 9