Question

3 bells ring at 4,7and 14 minall three bell rang at 6am when will the ring togeather again

Answer 1

The intervals of ringing of these 3 bells are 4,7 and 14 minutes. 
so, Minimum time after which these all 3 bells will ring = LCM(4,7,14) = 28 min. 
so, After 28 minutes , these all 3 bells will ring together. 
And, so, these bells will ring together at 6:28 am.

Answer 2

LCM of 4,7,14 = 28

Given three bells ring at 6 AM,

So they will ring together at 6:28 AM