Can you please explain this question? thank you

On Thursday 3rd November Annabel writes to Ben saying: "I will sell you my red Ford Fiesta car for $2,000. If I do not hear from you by 5 p.m. Monday 7th November I will assume we have a deal, and I will deliver the car to you on Wednesday 9th November". Advise Ben, giving reasons for your answers, in ALL of the following ALTERNATIVE circumstances: (i) Ben does not contact Annabel but Annabel, in accordance with the terms of her offer, delivers the car to him on Wednesday 9th November. Ben refuses to pay for the car or accept delivery of it. (ii) Ben posts a letter back to Annabel on Friday 4th November saying: "I am interested in buying your Ford car but think $2,000 is rather expensive. I would pay $1,800 for it." Annabel receives Ben's letter on the following Monday morning. On Sunday 6th November Ben telephones Annabel and accepts her 3rd November offer to sell her car for $2,000 but Annabel tells him that she sold it to someone else the day before