You need to word this question a bit better. You said he mostly used the same number each time, meaning some bunches had a different number - meaning it could be practically any answer between 2-9.
Assuming each bunch had the same number, however, we can find and exact answer.
The way to do this is to see which of the possible choices go into 45 evenly.
45 is not even, therefore it cannot be 2
4+5=9***
4 is even and the ones digit is not 04 or 8 so it cannot be 4
The ones digit is 5***
It is not divisible by 2 or 3 so I cannot be 6
It is not divisible by 7
It is not divisible by 8
4+5=9. 9 is divisible by 9***
The possible numbers in each bunch are 3, 5, and 9