If 31z5 is a multiple of 3, where z is a digit, what might be the values of z?

IF 31z5 is a multiple of 3,where z is a digit, what might be the value of z?

If 31z5 is a multiple of 3,where , z is a digit,what might be the value of z.

If 13 z4 is a multiple of 6, where z is a digit what might be the value of ?

If 13z4 is a multiple of 6, where z is a digit what might be the value of?

If 24y5 is a multiple of 3, where y is a digit, what might be the value of y?

If 24 y5 is a multiple of 3, where y is a digit , what might be the value of y ?

If 31z5 is a multiple of 9, where z is a digit, what is the value of z?

If 31z5 is a multiple of 9, where z is a digit, what is the value of z? You will find that there are two answers for the last problem. Why is this so?