_.._.'___. _ Jack offers to mow Jill's lawn. Because Jill plans to host a Canada Day barbecue on July 1, she agrees to pay Jack $50.00 if the lawn is mowed by June 29. On June 30, she nds that the lawn has still not been mowed. Jack informs her that it has been raining, and that cutting wet grass is not productive because it takes a lot more time and maintenance to keep his machine running. He will wait until the rain stops and the grass is dried. Jill, who is anxious to have enough time to set up tables and chairs for her barbecue, promises Jack that if he mows the lawn that day, she will give him an additional $20.00. Jack mows the lawn but Jill refuses to pay him the additional $20.00