Answer: They can offer parol evidence to clarify the clerical error
Explanation: Considering that an agreement was reached on the hourly rate of $ 20 and forty hours a week, it is obvious that this was a mistake when writing the contract, that is, a clerical error. The rule of parol evidence can be used to correct this error, because this rule regulates what types of evidence can be provided as confirmation of a clerical error to correct it. This rule is, in fact, used in contractual disputes, in order to correct the clerical error by determining the actual terms of the contract, which were reached by agreement. This parol evidence actually preserves the integrity of the contract because it prevents any alteration of documents i.e contracts and prevents the meaning of the document / contract from changing caused by mistake and a like.