Relative velocity: Boat problem

A river flows due West at a speed of 2.5 metres per second and has a constant width of 1 km. You want to cross the river from point A (South) to a point B (North) directly opposite with a motor boat that can manage to a speed of 5 metres per second. 1. Move the sliders to change the magnitude and direction of vectors. 2. Click the 'Start' button to activate the motion of the boat. 3. Click the 'Reset' button to put back the boat to its original position. 4. You can also change the width of the river. Chose a number between 5 and 1000.
a) If you head out pointing your boat at an angle of 90 degrees to the bank. How long does it take to get from point A to point B? b) After crossing the river you realised that it took longer than expected. In what direction should you point you motor boat in order to reduce the time to cross the river? How long will it take you to get from point A to point B? Is it a better time?