There are a total of 30 students in class 2C. They took two maths exams and all students participated. 25 students passed the first exam, while 12 students failed the second exam. There are only 3 students who passed the second exam but failed the first. How many students passed only the first exam? 
Overseas Competition->Knowledge Point->Counting Modules->Inclusion-Exclusion Principle->Inclusion-Exclusion Principle for Two Sets