3: [5 marks] A tennis ball is thrown into the lake at B. A dog runs along the beach a distance d before swimming directly to the ball. Find the distance d in order to minimize the time required to get the ball, if the dog can run at 6.40 m/s and swim at 1.95 m/s (Hint. Graph the function t = f(d) over the domain 0..30) A 30 m B 10 m