On Monday, Gary sent an email to Luis offering to sell his Playstation 5 (PS5) for $900. Luis replied (in another email) that he needed some time as he is waiting to be paid from his Monash College teaching. Gary, replied "don't worry - let me know by Thursday 6.00 pm. I'll keep the offer open until then" On Wednesday, Gary sold the PS5 to Andrew. On Thursday morning, Luis has been paid for his teaching work at Monash College, and, in a state of great excitement, calls Gary. Before Gary can tell Luis the PS5 has been sold to Andrew, Luis accepts the offer in these words "Gary, I accept - assuming you will also include a second controller!" Gary then informs him that he has sold the PS5 to Andrew. Luis is shocked. He drives straight to your office and asks if Gary can do that. Please advise him. In your advice, indicate whether: 1. Gary's promise that he would keep the offer open until Thursday at 6.00 pm is enforceable. 2. Assuming the offer is open on Thursday, indicate whether Luis's acceptance is valid.