1. **Problem Statement:** Solve question 11 (not provided in the prompt). Since question 11 is missing, I cannot solve it directly. 2. **Explanation:** To solve any set theory problem, we use the basic operations and definitions: - Union ($A \cup B$): all elements in $A$ or $B$ or both. - Intersection ($A \cap B$): elements common to both $A$ and $B$. - Complement ($A'$): elements not in $A$ but in the universal set. - Cardinality ($n(A)$): number of elements in set $A$. 3. **Note:** Without the exact statement of question 11, I cannot provide a solution. **Final answer:** Please provide the exact text of question 11 to proceed with the solution.