A sailboat race course consists of four legs, defined by the displacement vectors , , , and , as the drawing indicates. The magnitudes of the first three vectors are A = 2.90 km, B = 5.50 km, and C = 4.70 km. The finish line of the course coincides with the starting line. Using the data in the drawing, find
(a) the distance of the fourth leg and
(b) the angle.