Bell1 : tolls at t = 0seconds, 7s, 14s, 21s....

2" 0s, 8s, 16s, 24s,...

3: 0,11,22, 33s,...

4: 0, 12, 24,36,48s,...

LCM of 7s , 8s ,11s ,12 is : 7 * 2 *2*2 *11 * 3 = 1848 sec = 30 min and 48 seconds.

so we add 30 m 48 sec to the previous time instant that they tolled together.

next time all the bells will toll together will be at 9 h 30min 48 sec

next time it will be 10 h 1 min 36 sec

next it will be at 10 h 32 min 24 sec

next it will be at 11 h 3 min 12 sec

next it will be at 11 h 34 min 0 sec

next it will be at 12 h 04 min 48 sec.. this is after 3 hrs from 9 am.

===> to do it simply: in 180 minutes = 3 hrs, they toll together

= 180 min / 30min 48sec times

* = 5.84 times that is 5 times.*