please help me in these questions of business law

City University of Hong Kong School of Law LW2903 Business and Law - Assignment On Friday 17 January 2020, Ada put up a poster at her shop to advertise the sale of KF94 face masks. Eric and Jason saw the poster and inquired the availability of these masks. They were told that these masks are sold as a pack of 20 for $330 per pack - to be delivered late February. Eric placed an order for 3 packs of masks. He was asked to pay 50% deposit at the shop and was told to pay the remaining 50% on delivery. Jason was also interested and asked if Ada can give him a discount for buying 50 packs. Ada said she can give Jason a 5% discount for ordering 50 packs, but he must pay the full amount by Friday, 24 January 2020, 3:00 pm. Otherwise, she will charge him the normal price of $330 a pack. Jason said he will think about it. Ada also mentioned she is travelling to the Mainland to visit her relatives over the Lunar New Year - she gave Jason her bank account number just in case he decides to buy 50 packs of masks. Later that afternoon, Eric messaged his friend Kelvin to inform him that he can order these KP94 masks overseas. As Kelvin went to London for a business trip, he faxed Ada from London and placed an order for 100 packs of masks to be delivered to his London office at the end of February. Ada agreed and faxed Kelvin back and told him to transfer $33000 to her bank account. Kelvin transferred $33000 to Ada on the same day. On 1 February, Jason decided to order 50 packs of masks from Ada and he transferred $15,675 (the discounted price) to Ada's bank account. Jason called Ada and left a message on her mobile phone and said "This is Jason, I would like to order 50 packs of KF94 masks from you. Since I am buying 50 packs of KF94 masks, I have transferred $15.675 (with the 5% discount) to your bank account just now. If I do not hear from you by Monday 3 February, I assume you are fine with this order". After the Lunar New Year, Ada informed Jason that his order came too late and she will transfer $15,675 back to Jason. She also called Eric and Kelvin to inform them of the delay with the shipment of the masks. Eric, Jason and Kelvin are not very happy about this. They want to know what they can do