Answer:
7.92 m/s
Step-by-step explanation:
 = Mass of raindrop =
 = Mass of raindrop = 

 = Mass of mosquito
 = Mass of mosquito
 = Initial Velocity of raindrop = 8.1 m/s
 = Initial Velocity of raindrop = 8.1 m/s
 = Initial Velocity of mosquito = 0 m/s
 = Initial Velocity of mosquito = 0 m/s
 = Velocity of center of mass
 = Velocity of center of mass
For elastic collision

Hence, the velocity of the attached mosquito, falling immediately afterward is 7.92 m/s