Calculate the slope by dividing the change in rise over the change in the run of the line. (If you have already calculated the slope, skip this step.) To find the change in the rise, subtract the first y-coordinate from the second y-coordinate. To find the change in the run, subtract the first x-coordinate from the second x-coordinate. Then divide the change in the rise by the change in the run. For example, if your points are (-2, -4) and (3, 11), subtract -2 from 3 to get 5, and subtract -4 from 11 to get 15. Then divide 5 by 15 to find that the slope equals 1/3.
Multiply the slope by the x-coordinate of the first point on the line. In this example, multiply 1/3 by -2 to get -2/3.
Subtract the result from the y-coordinate of the same point to find the vertical intercept. In this example, subtract -2/3 from -4 to find that the vertical intercept equals -3.33.