you have to use point slope form
point slope form: y - y1 = m(x - x1)
x1 and y1 are the x and y values of the given point
m is the slope
so, just plug in the numbers:
y-3 = -2(x + 8)
now solve to put into slope intercept form (y = mx + b)
y-3 = -2x - 16
ANSWER: y = -2x -13