[填空题]
A tsunami of wavelengthfc7x)b7ldmeg+)v (o z 0moj,t 250 2j9, 1l0lovvoh ghqcprj d ;77km and velocity 750 km/h travels across the Pacific Oceanpr0; doqlgo7v 7hjv2c9 1j,hl. As it approaches Hawaii, people observe an unusual decrease of sea level in the harbors. Approximately how much time do they have to run to safety? (In the absence of knowledge and warning, people have died during tsunamis, some of them attracted to the shore to see stranded fishes and boats.) min
