Answer:
Consideration contract.
Explanation:
Consideration is basically the fact that Lewis never offered something in consideration to Tuan for his offer to pay the $3,000, this means that both parties need to have a benefit from the agreement and both should have a detriment, if only one party has a benefit that is considered a gift, and the law can´t force someone to gift something. This is why Tuan claim is correct and he isn´t forced to pay the $3,000 to Lewis.