Answer:
I believe the next time both bells will ring at the same time is at 6:30PM.
Explanation:
If the bells toll together at 6:00PM, the next time they toll together again should be at 6:30PM.(this is just how it works in my mind) if you add 15 to 15,, you get 30, right? And if you add 10+10=10, you get 30, right? And since 30 is a common number that both 10 and 30 can go into,, and is the lowest number both can go into,, it has to be the answer.