The legal point in question is whether Leila advertisement constitutes a binding contract and that she go can back on her promise of paying the reward $50 to Julie for returning the gold chain and locket to her. Relevant principle of law relating to this issue is that an advertisement made to the world at large is considered as a unilateral offer and not an invitation to treat.
The reason for this rule is that making an advertisement to the world at large, any person who follows the instructions has accepted the offer without further bargaining. For instance, selling a grand piano for $10,000 if any person comes to the offeror on the 1st Sunday morning of the month. In the case of Gunthing v Lynn (1831) 2B & AD 232, Lynn offered to buy a
horse from Guthing under a condition that if the horse brings him luck, Guthing will pay ? 5 to Lynn. Similar to the case of Leila advertisement does not state any notice of accepting the offer by calling first. The above principle was clearly stated in the case of Carlill v Carbolic Smoke Ball Co (1893) 1 QB 256, an advertisement was also made to the world at large for paying anyone who brought the product and still got flu.
Would mean that the offer is as promise for the performance of an act made to the whole world for this case is a binding contract. The principle in the case of was further endorse in K Murugesu v Nadarajah  2 MLJ 82, one party makes a promise in return for the performance of an act. The case of Carlill v Carbolic Smoke Ball Co (IBID) is an example of executed consideration where the defendants advertised the promise of a reward for persons to use their smoke balls in a certain manner.
Applying the principle of law, it can be argue that putting an advertisement in the newspaper to the world at large is a unilateral offer. Leila will not be able to ascertain as to who will take up the offer. The person who fulfills the requirement of finding and returning the lost item to Leila is entitled to the $50 reward. Julie who found and returned the gold locket and chain is counted as an acceptance of the offer, with the consequences that a contract exists both parties.
Therefore, Julie has the right of claiming the sum of money that she had invest in reaching to Leila destination. Leila claims that Julie should have called first before returning, however this argument is invalid as this term is not specified in the advertisement. Furthermore, by returning the items, the elements of the contract are satisfied and it need not be achieved through calling. As a counter Argument, if Leila advertisement is only an invitation to treat, there will be no binding contract between Leila and Julie.