On August 1 Dave borrows $10,000.00 from Jill. It is agreed that Dave will repay Jill the full amount on September 1, 2015. Dave fancies himself as a canny investor and thinks he can make a few trades on the share market and make a profit within the month. He uses the money borrowed from Jill to buy shares Unfortunately for Dave, the share market is very volatile during August and some of his trades have made considerable losses. As a result, on September 1 the value of Dave's shares is only $7000.00. Dave speaks to Jill that day asking if he can pay her back the loan at a later date, so he can recoup his losses on the share market. Jill replies that he cannot. Dave tells Jill that if she wants the money immediately, he can only afford to pay her $7000.00 due to his losses on the share market. He asks Jill whether she will accept $7000.00 as a full settlement of the debt. Jill accepts, Dave sells his shares and pays her $7000.00.A week later, Jill contacts Dave and says that she has changed her mind and demands that Dave pays her an additional $3000.00. Dave protests, telling Jill that she promised to accept the $7000.00 instead of the full amount owed, but Jill insists that he pay her the rest.

Advise Dave whether Jill's demand is legally enforceable