Ms. Theresa Lau, posted the following advertisement in a promotion leaet to the public in a shopping center in HK: \"Do you want to pass the HKDSE Math examination with Level Five or above? If you still cannot pass the HKDSE Math examination with Level Five or above after participating ALL tutorial lessons offered by me, you will get the whole refund of tuition fee of HK$3,000 plus HK$1,000. I have already deposited HK$150,000 of guarantee with a bank to show my sincerity to keep my promise.\" The nephew of Theresa, John, participated ALL tutorial lessons with Theresa, but without any payment. He took HKDSE but still cannot pass the HKDSE math examination with Level Five or above. Theresa asked his nephew to pay the tuition fee to her. But John said that they were family members and only made social agreement, and therefore, he did not have any duty to pay to Theresa. Besides, he did not pass the HKDSE math examination, so he refused to make payment. Under contract law principles, provide legal advice to both Theresa and John