When the boat moves on the surface of the water the resistance force of the environment F is directly proportional to the speed v (

, where

- coefficient of proportionality). At the moment of the engine shutdown the outboard motorboat is moving at a speed of 216 m/min., and 1 min. later it’s speed is equal to 108 m/min. 3 min. after the engine shutdown the outboard motorboat will be moving at a speed of ______ m/min.