The question asks to determine $n(D)$, where the set $D = \{6\}$.

In this context, $n(D)$ refers to the cardinality of the set $D$, which means the number of elements in the set.

Given that the set $D$ contains only one element, the number 6, we can conclude:

$n(D) = 1$

Would you like further clarification or additional details on set theory?

Here are five related questions:

1. What is the cardinality of an empty set?
2. How do you determine the cardinality of a set with multiple elements?
3. What is the difference between a subset and a proper subset?
4. How can you represent the union and intersection of two sets?
5. What is a power set, and how is its cardinality calculated?

Tip: The cardinality of a set is always the count of unique elements within it. Repeated elements do not increase the count.