18. Show that the vectors (-1, 2, 6), (3, 2, -1) and (7, 10, 9) lie on the same plane. 19. The vertices of quadrilateral ABCD are given as A(0, 3, 5), B(3, -1, 17), C(4, 1, 3) and D(7, -3, 15). Prove that ABCD is a parallelogram.20. A sign is hanging from a storefront. The two ropes holding it are fixed at angles of 25 and 35 with the horizontal. If the sign has a weight of 1150 N, what is the tension in each rope? 21. A plane needs to travel to a location 1550 km away, at a direction [N30E]. The plane flies at a velocity of 625 km/hr, and there is a wind of 80 km/hr at a direction [N10W]. a. What heading should the pilot take to arrive at the destination? b. How long will it take? 22. Find the area of the triangle defined by the following three points: A(2, 4, 5), B(5, 0, 6) and C(1, -3, 4)