A number is dividable by 9 if the number is a multiple of 9
for example, 81 is a multiple of 9 and also it is dividable by 9
You can check any number if you divide this number between 9
For example
1234/9 =137.11
because you have decimal number is an indication that this number is not divisible by 9
5832/9=648
because we have an integer we can say 5832 is dividable by 9