$\"\"$

Constant current speed of river is $\"\"$ .

Find at what angle to a boat dock should a motorboat capable of maintaining a constant speed of $\"\"$ .

Diagram of the situation:

$\"\"$

Observe the figure:

$\"\"$

Width of the river is $\"\"$ km.

Find resultant speed of the boat $\"\"$ due to constant current of river.

Observe the figure:

$\"\"$

Resultant speed of the boat is $\"\"$ kmph.

$\"\"$ .

Find the time required to boat to cross the river.

$\"\"$

$\"\"$ .

$\"\"$

$\"\"$ .

Time required to boat to cross the river is $\"\"$ .