PREP2-12

Sets A, B, and C have some elements in common.  If 16 elements are in both A and B, 17 elements are in both A and C,
and 18 elements are in both B and C, how many elements do all three of the sets A, B, and C have in common?
 
(1) Of the 16 elements that are in both A and B, 9 elements are also in C.
 
(2) A has 25 elements, B has 30 elements, and C has 35 elements. 
 大家帮忙给算下吧，条件二确实不可以算吗，我算了下，貌似数值不对。。。

[AUBUC]=A+B+C-AC-AB-BC+ABC

要求ABC,要知道以上的除自身以外的式子,

可是[AUBUC]不知道...