Hoping I can get some help with the following homework question please?

In IRAC format, with reference to relevant case law discuss whether:

there is a contract and, if so, who made the offer

it would make any difference if Harry, worried about possible delays in the postal service, sent his reply by email instead

In January, Sally, a top fashion diamond jewellery designer who lives in London, met Harry, a rich diamond buyer, also from London, at a diamond exhibition in Paris. Over a lovely lunch, they discussed what they had seen at the exhibition and established a good friendship and agreed to stay in touch. Harry has a house in London and a house in Paris and spends several months of the year in each.

They start writing regularly to each other and in May, Harry writes to Sally saying that he really likes her ring designs, especially one with a blue diamond and would love to have it. Sally replies by mail and says that she's delighted that he likes it and can supply it to him but that another buyer is interested in it and she must have a reply from him confirming his interest within three (3) days. He replies the next day by post saying that he accepts her offer and will pay her $100,000. The letter is delayed and Sally ends up selling the ring to the other buyer.