This is College Physics Answers with Shaun Dychko. The distance something travels equals its speed times time. So we can solve for time by dividing both sides by speed. So <i>t</i> is distance over speed. So that's 12,000 kilometers written as times ten to the three meters, divided by 15 meters per second is the speed of this wave. This works out to eight times ten to the five seconds which is not a good unit for our intuition so it's easier to think about days. So multiply this by one hour for every 3600 seconds times by one day for every 24 hours. This works out to 9.26 days for this wave to reach the California coast.