[填空题]
A sailor strikes the side of his shikw3yctr9 o-,vp just below the surface of iw :q8 jmi+ipes4ft9q) 8w .ozthe sea. He hears the echo of the wave reflected from the ocean floor directly below 3.0 s laterozi8: ip4e+wtfq iw jm)8q.9s . How deep is the ocean at this point? m