for 2 points A(xa;ya) and B(xb;yb)
the slope is (yb - ya) / (xb - xa)
here
the slope = 4 = (17-r) / (4-(-1))
(17-r) / 5 = 4
17 - r = 20
r = 17 - 20
r = - 3
point (-1 ; -3)
