To transform the equation \( 4x + y = -12 \) into slope-intercept form, which is \( y = mx + b \) where \( m \) is the slope and \( b \) is the y-intercept, we can isolate \( y \).
Starting with the original equation:
\[ 4x + y = -12 \]
Subtract \( 4x \) from both sides:
\[ y = -4x - 12 \]
Now we have the equation in slope-intercept form, \( y = -4x - 12 \).
Thus, the correct answer is:
C. \( y = -4x - 12 \)