c.1.
P = [-15, 10, 14] + r·([-3, 16, 8] - [-15, 10, 14]) = [x, y, 0] --> x = 13 ∧ y = 24 ∧ r = 7/3
Q = [-15, 10, 14] + r·([-27, 16, 8] - [-15, 10, 14]) = [x, y, 0] → x = -43 ∧ y = 24 ∧ r = 7/3
c.2.
([-15, 10, 14] + r·([-43, 24, 0] - [-15, 10, 14]) - [-27, 16, 0])*([-43, 24, 0] - [-15, 10, 14]) = 0 --> r = 11/21 → T = [-15, 10, 14] + 11/21·([-43, 24, 0] - [-15, 10, 14]) = [- 89/3, 52/3, 20/3]