<image>(2013 Spring, Longfeng District School Level Final Exam) The image shows the sales situation of a supermarket over four days. ______
First, understand the statistical chart above, then answer the following questions:
(1) The sales amount was the highest on the ____ day and the lowest on the ____ day.
(2) What is the average sales amount over these four days in ten thousand yuan? Can you write out the formula?
(3) The sales amount on the fifth day might be a bit higher than the average sales amount of the previous days, possibly ____ ten thousand yuan.