Week 3 Challenge Problem 19 Inquiry

In week 3's challenge question 19, I am not sure if this is a mistake. The answer, you say, is the number of multiples of three between 1 and 100. But if we take x=3, 3 and 0 cannot have the status of being relatively prime or not because 0 isn't defined to be (not) relatively prime to any number, according to Google searching afterward. So the answer should be 331, or 32. Can someone clear things up for me? Thanks a lot.