Final answer:
The provided information does not specify the difference in the number of states requiring personal finance courses in public high schools between 2007 and 2009, preventing a definitive answer to the student's question.
Step-by-step explanation:
The difference between the number of states requiring public high schools to offer a personal finance course in 2007 and 2009 is not explicitly mentioned in the information provided. Therefore, we are unable to determine which option - a) 9 states in 2007 and 13 states in 2009, b) 9 states in 2007 and 15 states in 2009, c) 7 states in 2007 and 13 states in 2009, or d) 13 states in 2007 and 15 states in 2009 - best describes the change in state requirements for personal finance courses during that period. Without additional context or a specific figure cited in the article excerpts, giving an accurate answer is not feasible.