Final answer:
Quotation marks around 'new' in the given sentence indicate irony or sarcasm, suggesting that the car is not truly new.
Step-by-step explanation:
In the sentence "Landon's "new" car is nine years old and has 75,000 miles on it," the quotation marks around new serve a specific function. They indicate that the word is being used ironically or with sarcasm. Quotation marks in this context suggest that the car is not new in the traditional sense of the word, but is being labeled as 'new' in a tongue-in-cheek or mocking way. This use of quotation marks conveys a different meaning than the literal interpretation and adds nuance to the sentence.