First find the slope which we get by dividing the difference of the y coords of the given points by the difference of the x coords: (-9-7)/(3-(-1))=-16/4=-4.
Then we take either point to build the equation of the line:
Using point (-1,7) we get:
y-7=-4(x+1), y-7=-4x-4, y=-4x+3 in slope-intercept form. The other point automatically fits this equation: -9=-4×3+3.