17.If A = (1, 2, 4), B = (3, 4 1), and A + B + C =(3, 1, -2), what is C ? Explain. [4 Marks] 18. Describe the difference between airspeed and groundspeed. [3 Marks] 19. A 500 N sign is supported by a cable that makes a 45 angle with the vertical wall and is held out from the wall by a rigid pole that is perpendicular to the wall. Determine the tension in the cable and the compression in the pole. [4 Marks