The average purchase price of a white duck is between 7- 12 yuan. After the roast duck is cooked, the retail price of each duck is between 15-28 yuan, and the profit is between 8- 16 yuan. According to conservative estimation, the store can sell 50 ducks every day, and the daily gross profit is between 400-800 yuan. According to the daily 500 yuan, a month is 500x30 = 15000, and a year is1500x12 =180000. After deducting taxes and rent, the annual profit shall not be less than140,000 yuan.