21. Given x = (2, 5), y = (-5, 12) find the scalar projection of x on y. [2 Marks] 22. If (-1, 3, 5) x (0, a, 1) = (-2, 1, -1), determine a. [2 Marks] 23. Given u = [1, 7, 9] and, v = [-2, 5, -3] and w = [4, -6, 8]. a) Find the angle between u and w. [3 Marks] b) Are the vectors u and i and w coplanar? Show your answer algebraically. [3 Marks]