A soccer player kicks a rock horizontally off a 35.0 m high cliff into a pool of water. If the player hears the sound of the splash 2.84 s later,

A soccer player kicks a rock horizontally off a 35.0 m high cliff into a pool of water. If the player hears the sound of the splash 2.84 s later, what was the initial speed given to the rock? Assume the speed of sound in air to be 343 m/s.