일반물리학 1 — Motion in Two and Three Dimensions: Problem 80

80 A 200 m wide river flows due east at a uniform speed of 2.5 m/s. A boat with a speed of 8.0 m/s relative to the water leaves the south bank pointed in a direction 30° west of north. What are the (a) magnitude and (b) direction of the boat’s velocity relative to the ground? (c) How long does the boat take to cross the river?