An earthquake occurs in the gulf of Alaska, 3600 km from Hawaii. The quake's seismic waves travel at about 560 kilometers per minute. The quake...

Seismic waves have to travel a distance of 3600 km and the speed of seismic waves is 560 km/min. Hence the seismic waves will reach Hawaii in :

time = distance/speed = 3600 km/560 km/min = 6.43 minutes.

The tsunami travels at a speed of 640 km/hr and will reach Hawaai in:

time of tsunami travel = 3600 km/640 km/hr = 5.625 hours or 337.5 minutes.

Thus, Hawaii will receive the earthquake, about 331 minutes (= 337.5 - 6.43) or 5.52 hours before it will be hit by the tsunami.

Thus, the islands of Hawaii will have an advance warning of about 5.52 hours of impending arrival of a possible tsunami. And that is the time available for preparing for the possible damages caused by the tsunami and clearing out the beaches and other coastal regions, etc.

Hope this helps.