All you do is plug in the x and y in the point to the equation, y = mx + b. Since the coordinate is (5, -3), this in the equation would look like -3 = -.5(5) +b. (all you need to find is the y-intercept, or b.) Solve it out to get -3 = -2.5 + b. Add 2.5 to each side of the equation, you're left with b = -.5. Now, put that back into the original equation, and get y = -.5x -.5. I think this is right, you can go back through and check once more if you'd like.
