We can use trigonometry to solve this problem.
First, we need to find the horizontal component of the boat's velocity. This is given by:
horizontal velocity = sailboat speed x cos(wind angle)
horizontal velocity = 17.9 m/s x cos(19.6°)
horizontal velocity = 16.9 m/s
Next, we need to find how long it takes for the boat to cross the river. This is given by:
time to cross = distance / vertical velocity
time to cross = 43.3 m / 17.9 m/s
time to cross = 2.42 s
Finally, we can find how far downstream the boat will be at the end of this time. This is given by:
downstream distance = time to cross x horizontal velocity
downstream distance = 2.42 s x 16.9 m/s
downstream distance = 40.9 m
Therefore, the sailboat will be approximately 40.9 meters downstream when it reaches the other side of the river.