The bells at kings school ring every 6 mins. at queens school the bell ring every 5 mins. at princess school the bell rings every 9mins. all three bells ring together at 8: 30am. when is the next time the bells of the three schools will ring together?

Even though it is throws time in there, it is a simple lowest common multiple problem.  Just think the interval numbers separate from the start time.   

using the table method is the easiest way to find this.  I tried copying a table i made but could not.  you will find the LCM of 5, 6, and 9 is 90.  so 8:30am plus 90 minutes would be 10:00am