7. The number of sets $X$ that satisfy the condition $\{1,2,3\} \subseteq X \subseteq\{1,2,3,4,5,6\}$ is
7. 8. Hint: $X$ must include the three elements $1,2,3$, while the three numbers $4,5,6$ may or may not belong to $X$. Each number has 2 possibilities, so the total number of different $X$ is $2^{3}=8$.