The points 6,4 and 9,r lie on a line with slope 3. Find the missing coordinate r. Slope = (y2 - y1)/(x2 - x1) Plugging in our numbers, we get: 3 = (r - 4)/(9 - 6) 3 = (r - 4)/3 Cross multiply: r - 4 = 9 Add 4 to each side: r = 13