Answer:
4) Willis breached the contract, but the breach was not material.
Step-by-step explanation:
Willis made a mistake when he was installing the floor and faucets in the powder room. But the mistake was not substantial, if you consider that the contract for building the house was worth $300,000 and it costs only $3000 to fix the mistake (that is only a 0.1%).
Under the substantial performance doctrine, we can consider that Willis performed his part of the contract and Robert must pay him for building the house. Substantial performance refers to a situation where a contact is not 100% complete, but almost 100% complete. In this case the contract is 99.9% complete, so Robert cannot use the powder room as an excuse to not pay Willis for his work.