Donna is an accountant and decides to do her friend mike a favor by filing his taxes for free. mike is very and tells donna "i will pay you $500 for being so kind and generous! " mike fails to keep his promise and does not pay donna the $500. donna then brings an action to have the promise enforced. will the court hold that a contract exists? a) yes, what mike did to donna was unjust and therefore the contract is enforceable. b) no, past consideration is no consideration at all. c) yes, due to the preexisting duty rule. d) no, it is an illusory promise and is no consideration at all.