ultrasonic

...that travel 1530 m/s in? seawater. how deep is the water directly below the vessel if the time delay of the echo to the ocean floor and back 5 s?

I'm 17 and my fone rings like in every 15-20 minutes. I don't want to put my mobile on silent because I won't be able to hear anyone calling. I want to set a cool ultrasonic ringtone for my mobile so that my parents won't get disturbed (they are in 30's) and only I will be able to hear it. The...