Final answer:
The statement that there is no consideration for William's promise to pay an increased amount per week is false. In contract law normally a modification must be supported by consideration but the enforceability of such a modification without new consideration depends on the specific circumstances and potentially the applicability of the UCC.
Step-by-step explanation:
When Michael and William contracted for Michael to mow William's lawn once a week for 20 weeks, at a price of $20 per week, they created an enforceable agreement. Later, they modified the contract such that Michael would continue to provide the same service but for a higher payment of $22 per week. The statement 'There is no consideration for William's promise' is false. In contract law, for a modification to be enforceable, there must be some form of additional consideration provided by the party receiving the benefit of the new terms. In this case, Michael is providing the same services as before, which may suggest there should be additional consideration from William for the increase in price to make it legally binding.
However, under the preexisting duty rule, a promise to do something that one is already legally obligated to do is not considered valid consideration for a new promise. The modification in this context may not have legally sufficient consideration unless there are new or different terms or if they are operating under the Uniform Commercial Code (UCC) which allows for contract modifications without new consideration under certain circumstances.