After three months, the price of gas falls to $2.33 per gallon. Buyer refuses to keep buying from Seller unless Seller lowers the price. Seller agrees. Two months later, the average price for gas goes up to $3.50 per gallon.
After beginning the job, Petra realizes that the house is really quite big, and she's not going to make enough profit, so she tells Bret she wants another $500 to finish the job. Bret.