put the equation into y = mx + b form...the slope will be in the m position
12x + 3y = -17....subtract 12x from both sides
3y = -12x - 17....now divide both sides by 3
y = (-12/3)x - 17/3....reduce when u can
y = -4x - 17/3
y = mx + b
y = -4x - 17/3.....and the number in the m position, (the slope) = -4