Here are the answers to your questions:
8. How does the third sentence ("That makes walking ...") support the central idea of the paragraph?
Answer: It points out that walking is a good introduction to exercise for beginners.
9. Identify the central idea of this paragraph.
Answer: Judy Blume has been a very busy and gifted writer. (explicit)
10. Explain whether the central idea is explicit or implicit in this paragraph.
Answer: It is explicit because it is directly stated in the paragraph.
11. Which of the following lists represents text evidence pieces that all support the central idea in this paragraph?
Answer: Many awards, can write for multiple audiences, 30 novels
12. Which sentence could be added to further support the central idea in this paragraph?
Answer: Averaging a book a year, Blume's many works have been sold around the world.
13. Based on the article title, what is the central idea of the article?
Answer: Philadelphians want to repeal the soda tax because it's immoral.
14. Which sentence could be added to further support the central idea?
Answer: The New River Gorge Bridge is a popular tourist attraction.
15. How does the author develop these two central ideas?
Answer: By describing the many ways gymnasts train and perform.