City B is 10 miles downstream from city A. City A is 5 miles south of the river, and city B is 20 miles north of the river. The river is 2 miles wide. Where should we build a bridge across the river...

City B is 10 miles downstream from city A. City A is 5 miles south of the river, and city B is 20 miles north of the river. The river is 2 miles wide. Where should we build a bridge across the river to make the travel distance between cities A and B as small as possible? Can you generalize this result?

I can swim 2 miles per hour and run 6 miles per hour. I am walking north along South Beach and see someone drowning 0.5 mile out in the ocean and 1 mile north of me. What combination of running and swimming is the quickest way to reach the swimmer?