An agreement between two parties that benefits them both is

An agreement between two parties that benefits them both is called a contract.

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Contract, is the right answer.

Explanation:

A contract is an authorized requisite agreement which catalogs and regulates the rights and obligations of the parties to the contract. A contract is licitly enforceable because it satisfies the terms and acquiescence of the bill. This generally includes the interchange of goods, services, money, or obligations of any of those.

demand is the need and oportunity to buy a given good or service.