John is a student of Social Science at University. He attends classes in various buildingsin Melbourne CBD. John recently turned 21yearsso his father gifted him a new advance version of Apple Computer. John loves his computer. He even sets screen saver whichsays"I love My Computer-John, Mobile: 044123456". Last Wednesday John was attending his class in Building 80, Floor 9, Room 12.Before the class ended, John got an urgent call from hishomeso he picked up his bag and rushed out of the class to go to his home straight away. However, he forgot to take his computer that was plugged for charging in the corner of the classroom.

Sam is a student of Information Technology at University. He went for his class in Building 80, Floor 9, Room 12 on the last Wednesday just after John's class ended. Sam found John's computer. When Samopenthe computer, he saw the message on screen: "I love My Computer-John, Mobile: 044123456". Catrina was sitting next to Sam in theclassand she also saw the message on the screen. She suggested Sam that he should call that number later and return that computer to the real owner. Sam kept the computer in his bag and went home after the class.

Later in the evening John realized that he left his computer in the classroom. He came back to the classroom immediately to look for his computer. Unfortunately, he did not see his computer in the classroom. Just to try his luck, he put up a notice on the door of the classroom saying "Any onewho finds my computer, please return it to me. I love it more than my life! I will pay you $300. Contact me on my mobile 044123456." He also put the same message on the "Lost and Found" page of theUniversity'swebsite as well as on his ownfacebooksite.

Catrina saw the message of John on the Lost and Found page of the University. She sent aWhatsappmessage on John's number saying "Don't worry mate! MyfrdSam has got your computer. He will contact you later. Your computer is safe. Careful with new and expensive computer mate---everybody is not nice like me!"

Same day, in the late night, Sam remembered about the computer and then he called the mobile number of John. On the other side John picked up the phone. John was very happy to know the good news about his computer. Sam and John exchanged their phone numbers and e-mail addresses and decided to meet on the next day (i.e.Thursday) at the Coffee shop located on the ground floor of the building 80.

When John metSamhe thanked him and collected his computer. After having coffee John took out $300 and said to Sam "Here is your reward." Sam said "What reward! I am a man with high integrity. I didn't expect any money from you. Don't break my heart!"

Immediately after finishing with Sam, John went to the classroom and took down the notice from the classroom door which he put up the last evening. He also announced on the Lost and Found webpage as well as on hisfacebooksaying "Sam found my computer. God bless him! He didn't even take the reward."

On Friday, Sam came to know from Catrina that John was offering a reward of $300 for that computer.SoSam wrote an e-mail to John saying "I just come to know that you were offering $300 as a reward to the finder of your computer. Since I found yourcomputeryou must give that reward to me. Yesterday, I thought you were giving money to me as a tip! I will meet you at the same place tomorrow at 11 am. Please bring my reward or else ------." John was very surprised to see that message and he was more worried about the threating tone of the e-mail.

On the same day Catrina also wrote aWhatsappmessage to John saying "I responded first and informed you about your computer so you must pay the reward to me. It will be very unfair if you pay my reward to anyone else. I need money to pay for my rent. My uncle is alawyerand I can take you even to the court for this matter."

What are John's obligations here? Is he is obliged to pay $300 to Sam,Catrinaor both?