M & M Flying Service, Inc. entered into a written contract with the Andalusia-Opp Airport Authority to run management and commercial activities from January 1, 1983, to December 31, 1987. The Authority came under new management on January 1, 1988. When the new management and M & M failed to agree on the terms of a renewal of M & M's contract, the Authority sought to stop M & M from operating at the airport. M & M argued that at the same time it had signed the management contract in 1983, it had also signed a 10-year lease, and that the Authority had orally promised that M & M could continue to operate commercial activities for the life of the lease.

The assignment is to represent M&M Flying Service. Support and prove that this company is right. Please provide an argument for your client that there is a valid, enforceable contract.