On the coast, there are three lighthouses.
The first light shines for 3 seconds then it is off for three seconds.
The second light shines for 4 seconds then it is off for 4 seconds.
The third light shines for 5 seconds then it is off for 5 seconds.
All three lights have just come on together.
When is the first time that all three of the lights will be off together?
When is the next time that all three lights will come on at exactly the same moment?