The following question has three statements. Study the question and the statements and decide which of the statement(s) is necessary to answer the question.

The average marks scored by a class is 72.5. Find the total number of students in the class.

I. Difference between the number of boys and number of girls is 12.

II. The average marks scored by the boys is 70.5.

III. The average marks scored by the girls is 75.5.