Jack owns a shop that sells furniture. He placed an advertisement in the Friday's edition of the local paper stating: "Sale on all furniture 25% discount. Offer valid for one day only - tomorrow Saturday- Cash Only". Nick saw previously a dining table with 6 chairs when he visited the shop during the week. However, he could not purchase it at that time because the prices was quite steep. He has in his possession the ID number and details of the dining table. When he saw the advertisement on Local paper, he immediately posted a letter of acceptance, since a 25% discount is a bargain for him.

On the Saturday of the sale, Diana saw a wooden stool and made an offer to Jack. Diana then asked Jack if he would take a cheque for her purchase, Jack advised her that he cannot accept any cheque - Cash only. On the following Monday morning, Nick's letter arrived.

In the context of the rules governing the creation of contracts:

(a) Describe the precise legal nature of Jack's advertisement;

(b) Explain whether Nick has any right of action against Jack;

c) Explain whether Diana has any right of action against Jack.