Sure,
"/" is indeed used to divide.
So: 4 / 2 is equal to 2
And:6 / 3 is also equal to 2

However when you use the % operation the result is equal to the remainder left after a division
So: 4 % 2 is equal to 0 because there is no remainder when you divide 4 by 2
However: 7 % 3 is equal to 1 because 1 is the remainder (3 X 2 )

I was able to get a solution to pass that only inserted a single comma. I think the tests need to be expanded for larger numbers EG: 234,234,2345,234.234234234