(a) The edges OP, OQ, and OR of a tetrahedron OPQR are vectors p, q, and r, respectively, where p = 2i + 4j, q = 2i - j + 3k, and r = 4i - 2j + 5k. Show that OP is perpendicular to the plane containing OQR. Express the volume of the tetrahedron in terms of p, q, and r, and hence calculate the volume. -b Referring to the figure below, i determine the angle between the diagonal AD of the cube and the edge AB, and also ii find the angle between the diagonal AD of the cube and the diagonal AC.