Directions: The following questions are accompanied by three statements (I), (II) and (III). You have to determine which statements(s) is/are sufficient/necessary to answer the following question.

A group of six students in a class noticed that the sum of their ages is 23 less than the square of a prime number. Then, find the average age of the group.

I. Two elder students have an average age of 27.5 years and one youngest student has the age of 20 years.

II. All students are between 19 years and 30 years of age.

III. The difference between the age of the youngest and eldest student is 8 years.