Final answer:
The slope of a line parallel to the line with the equation x + y = -4 is -1, as parallel lines have the same slope.
Step-by-step explanation:
To find the slope of a line parallel to the line whose equation is x + y = -4, first put the equation in slope-intercept form, which is y = mx + b, where m is the slope and b is the y-intercept. For the equation x + y = -4, we can rearrange it to y = -x - 4. The slope of this line is -1. Lines that are parallel to each other have the same slope. Therefore, the slope of a line parallel to the line x + y = -4 would also be -1.