Final answer:
Mary is neither a qualifying child nor a qualifying relative of her parents because she provides more than half of her own support and her parents provide less than half.
Step-by-step explanation:
The question at hand is deciding whether Mary is a qualifying child of her parents or a qualifying relative, given that she is a 21-year-old full-time student and her support is 60% provided by herself and 40% by her parents. According to IRS guidelines, a qualifying child must be under 24 if they are a full-time student, must live with the parent(s) for more than half of the year (with exceptions for school), and cannot provide more than half of their own support. Since Mary provides more than half of her own support, she does not meet the criterion to be considered a qualifying child. On the other hand, to be a qualifying relative, the individual cannot be a qualifying child, must either live with the taxpayer all year as a member of the household, or be related to the taxpayer in one of the ways listed by the IRS, and the taxpayer must provide more than half of the individual's support. Since Mary's parents provide less than half of her support, she cannot be considered a qualifying relative either. Therefore, the correct answer is that Mary is not a qualifying child of her parents and is not a qualifying relative.