Find the coordinates of the mid-points of the line segments joining the following pairs of points :

(i) (2, -3), (-6, 7)

(ii) (5, -11), (4, 3)

(iii) (a + 3, 5b), (2a - 1, 3b + 4).

The line segment joining the points A(3, 2) and B(5, 1) is divided at the points P in the ratio 1 : 2 and it lies on the line 3x - 18y + k = 0. Find the value of k.

Find the coordinates of the points of trisection of the line segment joining the points (3, -3) and (6, 9).