Hello, ally79!
Rower $\displaystyle A$ is stationary at the point $\displaystyle A$ adjacent to the river bank
when he spots an object floating down the river.
He estimates that the object is 50 m away and heading south at a speed of 3 m/s.
Assuming rower $\displaystyle A$ can sustain a rowing speed of 4 m/s,
1) Draw a diagram of the velocity vectors involved if rower $\displaystyle A$ is to intercept the object.
2) Calculate the direction with respect to the river bank he needs to row
(in degrees) in order to achieve his goal. Code:
N * B
 *
 * 
 * 
 50 *20° 3t
 * 
 * 
 * 
20°* * C
 * *
 *θ * 4t
* *
A *

We are given: .$\displaystyle \angle NAB = 20^o,\;AB = 50$
. . Note that: $\displaystyle \angle ABC = 20^o$
In $\displaystyle t$ seconds, $\displaystyle A$ has moved $\displaystyle 4t$ m to point $\displaystyle C.$
In $\displaystyle t $ seconds, $\displaystyle B$ has moved $\displaystyle 3t$ m to point $\displaystyle C. $
Let $\displaystyle \theta = \angle BAC$
We want $\displaystyle \angle NAC.$
Using the Law of Sines: .$\displaystyle \frac{\sin\theta}{3t} \:=\:\frac{\sin20^o}{4t} \quad\Rightarrow\quad \sin\theta \:=\:\frac{3\sin20^o}{4} \:=\:0.256515107$
Hence: .$\displaystyle \theta \:=\:14.86338095^o \:\approx\:14.86^o$
Therefore: .$\displaystyle \angle NAC \;=\;14.86^o + 20^o \;=\;\boxed{34.86^o}$
Edit: skeeter pointed out an error . . . *blush*
I forgot: the boat is also affected by the current.
I'll have to work on a corrected version.
Sorry . . .
.