You have a boat and you're trying to cross a river that has parallel banks. If there is no current in the river, the quickest way to cross is to aim your boat directly across the river

If the water is flowing down the river, how should you aim your boat to reach the far shore in the shortest time?

1. Angle the boat upstream, and go against the current, landing somewhere upstream.
2. Angle the boat upstream in such a way that you land at the point directly across from where you started.
3. Point your boat directly across the river and get carried some way downstream.
4. Angle your boat downstream and get carried even further downstream.

If the current in the river is 3 m/s and your boat can travel at 5 m/s relative to the water, how should you aim your boat so you land at the point directly across the river? If the river is 100 m wide, how long does it take you to cross?