Total students = 28
Students with brown eyes = 19
students wear glasses = 13
Not brown eyes or no glasses = 7
Not brown eyes = 28 - 19 = 9
Not wearing glasses = 28 - 13 = 15
Not brown eyes and wearing glasses = 15 - 9 = 6
Brown eyes and wearing glasses = 13 - 6 = 7 <==== answer