There are five classes in grade six in Qiancheng Primary School. 15 students in each class passed the calligraphy exam. Some students have studied calligraphy this year, but now they have studied calligraphy.
Solution: Suppose that X students have passed the exam this year.
5* 15+x= 105
x= 105- 15*5
x= 105-75
x=30
Thirty students passed the calligraphy exam this year.