The given case study involves Harry requesting information about the price of a ring from Sally. Sally responds with an offer to sell the ring at $100,000, which is open for three days. Harry accepts the offer through post on the next day. According to postal rules, the posting of the acceptance letter is deemed as acceptance by Sally. The mode of sending acceptance was not specified by Sally, so if Harry had responded through email instead of post, it would have been invalid and no contract would have formed. This document provides a detailed analysis of the formation of the contract using postal rules.