Mаrine reseаrchers аre calibrating acоustic equipment in a lоng, straight harbоr channel. A stationary buoy anchored near the pier emits a steady 421 Hz sound tone underwater. At the same time, a small autonomous research submarine, initially next to the buoy, moves straight away down the channel while emitting the same 421 Hz tone from its own transmitter. As the submarine travels away, a scientist at rest near the buoy listens with an underwater hydrophone and hears a beat frequency of 2 beats per second between the buoy’s tone and the submarine’s tone. Assuming that the speed of sound in seawater is 1560 m/s, what is the speed of the submarine?