Petty, a general contractor, made a series of purchases from Field Lumber Company. Field’s records showed a total price of $1,752.21. Petty admitted he owed $1,091.96, but denied liability for the difference of $660.25. He claimed the difference was a result of an unauthorized $292.60 purchase by an employee, plus related finance charges. Petty sent a check for $500 along with a letter stating that the check must be accepted in full settlement of the total claim or returned. Field phoned to say the lumber company required full payment, but nevertheless Field cashed the check and sued for the full balance it claimed was due. Can Field Lumber Company now recover the full amount? (Field Lumber Company v. Petty, 512 P.2d 764, Wash.)