Which of the following would NOT be considered an illegal contract?

The answer identifying a gambling loan in a state where gambling is legal is correct, as it reflects the principle that legality is determined by the laws of the jurisdiction in which the contract is made. In this case, since gambling is permitted under state law, a loan made for gambling purposes does not violate any legal stipulations, making it a legal contract.

In contrast, a loan contract with usurious interest would be illegal due to state laws prohibiting excessive interest rates. Similarly, a contract that restrains trade could violate antitrust laws, which are designed to encourage competition and prohibit monopolistic practices. Lastly, a contract that solicits someone to commit a crime is inherently illegal as it involves agreements to engage in unlawful activities, which the law does not recognize or enforce. These distinctions highlight why option A stands out as legal due to its compliance with state regulations regarding gambling.