You will need 15 buses but there will be 5 kids left over so, actually you need 16 buses.
We have to basically multiply:

And simplifying that we get

And since there can't be .35 person
So out final answer is
The elapsed time from starting at 10:10 and ending at 10:45, assuming the time of day is the same. Is 35 minutes. If it is not the same time of day, then it would be 12 hours and 35 minutes.