17. In a donation activity of "Caring for Students", all the students in Class 9 (1) took out their pocket money and donated enthusiastically. The amount of student donations is 5 yuan, 10 yuan, 15 yuan and 20 yuan respectively. According to the statistical data, two incomplete statistical charts are drawn.

(1) There are _ _ _ _ _ _ _ _ students in this class, and students donate in the form of _ _ _ _ _ _ _ _ _ _ _ _ _;

(2) Please complete the statistical chart in Figure ②;

(3) Calculate the average donation of the class?