CPM Homework Help : PC Problem 10-41

The current in a straight river is flowing so that if a motorboat travels upstream at an angle of $20°$ with a velocity of $15$ km/hr, it will land at a spot on the opposite shore directly opposite its starting point. Find the speed of the current.

Hint:

Draw a diagram.

Show diagram:

Right triangle comprised of rays, horizontal ray points right, labeled actual path of motorboat, vertical ray points down, labeled current, hypotenuse points up & right labeled 15 kilometers per hour, angle opposite vertical leg, labeled 20 degrees.

Use trigonometry to solve for the 'current'.