Andrew enters into a contract with his tax accountant, Jeff, to prepare his business tax return within four weeks of the end of the tax year. The contract provides that Jeff is to receive $1,500 for his work and specifies that time is of the essence since the cash flow of the business depends on a timely return. Three weeks after the end of the tax year Jeff calls Andrew saying that there may be delays in processing the tax return. He demands an extra $600 from Jeff "to make sure that the return is finished on time". Andrew is hesitant but agrees because he knows his cash-flow position is precarious. The return is finished on time and Andrew receives his tax refund accordingly. Andrew sends Jeff a cheque for $1,500. Jeff telephones and demands the extra $600 "as we agreed". Andrew refuses. Jeff then asks his solicitors to send a letter to Andrew threatening legal action if the $600 is not paid. Andrew agrees to pay Jeff $300 to drop the legal action. Advise Andrew as to whether he is under any obligation to pay either amount