Charles was a jewellery designer and placed the following advertisement in West Noon Post on 1 November 2021. For Sale Handmade "88-shaped" necklace on display HK$10,000 Come to my shop and buy it now! Telephone Charles 99991111 Email: cec123@bmail.com Shop address: Shop 123, iCircle On 2 November 2021, he also shared the advertisement with his friends and relatives in his social media, Instagam with his own message. Once-in-your-life handmade Jewellery for sale! "88-shaped" necklace HK$1,000. Anyone wishes to buy my handmade jewellery. Private message to my email ccc123@bmail.com" Telephone Charles 99991111 Shop address: Shop 123, iCircle On 5 November 2021, Charles joined the family gathering. Anne, Charles's girlfriend, read his post on Instagam and jokingly said that she was interested in buying his handmade jewellery as she had never received Charles's jewellery. Charles responded and said "Sure! You can come to my shop. I promise to give it to you for free." Anne laughed and posted the message "a done deal" on his Instagam post for her record. On 8 November 2021, Philip, Charles's friend, read his post on Instagam and found the handmade jewellery was so cheap. He decided to purchase the handmade jewellery but was told that the actual price was HK$10,000 in Charles's jewellery shop. Philip was angry and said that Charles had to sell his handmade jewellery for HK$1,000 in any event because this was Charles's mistake by typing the wrong price on Instagam. On 9 November 2021, Anne came to Charles's shop and planned to collect the handmade "88- shaped" necklace. However, Charles said that this necklace would be sold to the buyer and refused to give this necklace to her. Anne was very disappointed and wanted to enforce his promise made on 5 November 2021. (a) Advise Philip as to whether Charles is under a contractual duty to sell the jewellery for HK$1,000. (b) Advise Anne whether there is a valid contract between Anne and Charles. (18 marks) (12 marks)