Archie used to sell various vintage items in his retail shop and online platform. He wanted to sell the used Leicase rangefinder camera for HK$2,500. He displayed the camera in his retail shop to attract any potential buyer. He also shared different posts in his social platforms.

On 1 April 2021, Archie posted a message in Outstagram (OG).

Used Vintage Camera for sale. Good condition. HK$2,500. Welcome to try it! Private message to xyz321@zzmail.com, Archie.

Archie expected to promote his retail shop so he posted another message in Facecook.

Be my model! Used Leicase rangefinder camera and HK$1,000 is yours if you visit my retail shop, take a selfie with Leicase camera and share your selfie in my social media.

On 1 April 2021, impressed by Archies post in OG, Charlotte emailed to show her interest in buying Leicase camera and asked Archie if she could pay HK$2,500 by credit card in his retail shop.

Archie had received many responses after having posted the message on Facecook. On 1 April 2021, a 18-year-old student, Diana came to visit Archies shop.

Hi! I like your post on Facecook. I wish to have the used Leicase camera. I will upload my selfie to your Facecook today. Diana said to Archie.

Then Diana took a selfie with Leicase camera. She immediately uploaded her selfie to Archies Facecook in the hope of obtaining Leicase rangefinder camera.

On 3 April 2021, Archie met his relatives in his cousins birthday party. His auntie, Elaine told him that she had read his post in Facecook.

Wow! I love such kind of the vintage camera. Hey! I uploaded my selfie to your social media. Can I have the Leicase camera? she said. Sure! I promise to give you the vintage camera. Archie forced a smile and responded to Elaine.

On 4 April 2021, Archie emailed Charlotte that payment could not be made by credit card. If she was still interested in it, she could send him an email for the order confirmation.

On 5 April 2021, Charlotte did not want to miss a chance to buy the rare Leicase camera so she sent an email to Archie and wrote OK! I agree to buy it. Can I meet you and collect the camera at your shop on 6 April? Looking forward to hearing from you soon.

On 7 April 2021, after a week, Diana sent an email to remind Archie that she uploaded her selfie to his Facecook and urged him to give her the camera and HK$1,000. Archie was puzzled as to whether he was under a contractual duty to give her the camera.

On 7 April 2021, Archie joined a monthly family gathering and met Elaine again. She asked him when she could get Leicase camera. He refused to give the camera to her and jokingly said that he made fun of her on 3 April 2021. Elaine was very angry and wanted to enforce his promise.

Required:

(a) Advise whether there is a valid contract between Archie and Charlotte on 1 April or 5 April. (10 marks)

(b) Advise Diana as to whether she is entitled to have Leicase camera and HK$1,000. (17 marks)

(c) Advise Elaine. (6 marks)