What Angle Should a Boat Point Upstream to Cross a River Straight?

[agadag]

Homework Statement

A boat that can travel at 4.0 km/h in still water crosses a river with a current of 1.8 km/h. At what angle must the boat be pointed upstream to travel straight across the river? In other words, in what direction is the velocity of the boat relative to the water?

1. 27° upstream
2. 33° upstream
3. 37° upstream
4. 39° upstream

Homework Equations

V= D/T?

The Attempt at a Solution

i found a problem similar in the book but the answer doesn't make any sense. I have an exam over this material tomm and would really apppreciate if someone can demonstrate and help me understand the solution!

 

[rl.bhat]

Show your calculations.