Final answer:
Ned's attempt to cancel the contract will not be effective because Larry has detrimentally relied on Ned's offer.
Step-by-step explanation:
In the given scenario, Ned contracts to sell his boat to Larry and Larry builds a dock behind his house to keep his boat. Ned's subsequent attempt to cancel the contract will not be effective because Larry has detrimentally relied on Ned's offer. Detrimental reliance occurs when one party relies on the promise of another party to their detriment. In this case, Larry has built a dock in reliance on Ned's promise to sell the boat.