How does Helene Hanff use imagery in 84, Charing Cross Road?

The imagery is related to the exposition of the story. Helene Hanff is responding to an advertisement for a bookseller specializing in out-of-print books. Knowing nothing of Marks & Co. in London, she encloses a list of "her most pressing problems": copies of secondhand books she cannot find, and a request that they must be clean copies costing no more than $5.00. The books arrive safely, and with the help of a neighbor in Helene's New York apartment building, Helene is able to determine the cost in dollars per British pound.