In this case, we'll have to carry out several steps to find the solution. 
Step 01:
Data:
- x + y = - 7 
Step 02:
equation of the line: 
Slope-intercept form of the line
y = mx + b
- x + y = - 7 
y = x - 7 
slope = m = 1
y-intercept = b = - 7
The answer is: 
Slope-intercept form of the line: 
y = x - 7 
slope = 1
y-intercept = - 7