If the central angle is 20 degrees, that means that the arc of this circle takes up 1/18 of the circle's circumference. Because there are 360 degrees in a circle, we get 1/18 by dividing the part (20 degrees) over the whole (360 degrees)
Now that we know that, we do the same for the circumference measure by taking 1/18 of 6, which is 1/3
You were going in the right direction but the problem was that you needed to subtract and not add. The formula should be y-y1 / x-x1 iirc. Hope this helped.
