The universal set is $U = \{ x \mid x$ is a natural number not exceeding 9 $\}$, and two subsets of $U$ are $$A = \{ 3,6,7 \} , B = \{ a - 4,8,9 \}$$ If $$A \cap B ^ { C } = \{ 6,7 \}$$ find the value of the natural number $a$. [3 points]
The universal set is $U = \{ x \mid x$ is a natural number not exceeding 9 $\}$, and two subsets of $U$ are
$$A = \{ 3,6,7 \} , B = \{ a - 4,8,9 \}$$
If
$$A \cap B ^ { C } = \{ 6,7 \}$$
find the value of the natural number $a$. [3 points]