First we need to figure out the slope. We can do that using the equation (y2-y1)/(x2-x1). Substitute your numbers in for the xs and ys:
(-9-7)/(-4-0)=
-16/-4=
4
Now that we have the slope, we can figure out the intercept by using the equation y=mx+b and substituting one of the points in for x and y, the slope in for m, and solving for b.