The inequality given is $7 \leq x \leq 9$. You are asked to express this using interval notation and illustrate it on the real number line.

1. Interval Notation: The inequality $7 \leq x \leq 9$ means that $x$ can take any value between 7 and 9, inclusive of both endpoints. The interval notation for this is: $[7, 9]$ The square brackets indicate that the endpoints 7 and 9 are included in the interval.

2. Correct Graph: On the real number line, this interval is represented by a solid line between 7 and 9 with closed circles at both ends, indicating that the endpoints are included.

   Based on the image, Graph D correctly represents the inequality with a solid line between 7 and 9 and closed circles at both 7 and 9.

Would you like more details on how to solve similar inequalities, or do you have any further questions?

Here are five related questions you could explore:

1. How do you solve compound inequalities?
2. What is the difference between strict inequalities and non-strict inequalities in interval notation?
3. How do you represent inequalities with infinity in interval notation?
4. How do you solve inequalities involving absolute values?
5. What are the steps to graph inequalities with more complex expressions?

Tip: When using interval notation, always check if the inequality includes or excludes the endpoints—this determines whether to use parentheses or brackets.