You are attempting to row across a stream in your rowboat. Your paddling speed relative to still water is 3.0 m/s (i. e., if you were to paddle in water without a current, you would move with a speed of 3.0 m/s ). You head off by rowing directly north, across the stream.
Assume that the stream flows east at 4.0 m/s, determine how far downstream of your starting point you will finally reach the opposite shore if the stream is 6.0 meters wide.

8 m

Explanation:

Vertical component of the speed of the boat = 3.0 m/s

horizontal  component of the boat = 4 m/s

the rowboat traveled the length of the river which = 6.0 m

time taken to travel across the 6 m wide river = 6 m / 3 m/s = 2 s

the distance far downstream of the starting point = horizontal speed × time = 4 m/s × 2 = 8 m

here we know that ball will drop down by total distance 3.2 m

so here we know that

now using kinematics

now in the same time it will cover horizontal distance of 0.75 m

so speed of the ball will be

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west