What's negative multiples of 3 in set builder-notation

Multiples of 3 are {3, 6, 9, 12, 15, 18, 21, 24, 27, 30, …….} , these are all the multiples of 3.
Now, we are looking a negative multiple of 3, which means, we need to a negative value of 3 multiples.
=> -3 {-3, -6, -9, -12, -15, -18, -21, -24, -27, -30,…..} These are all the negative multiple of 3 in set builder notation.
Notice, that the numbers are of divisible by 3. Any number that Is divisible by 3 is called multiple of 3.

21/3 is the answer i believe