A snipped for removing items from an array

RemoveItemFromArray.cs

    public class Student
    {
        public string Name { get; set; }

        public enum Gender
        {
            Male, Female
        }

        public int Age { get; set; }
        public string[] Grades { get; set; }
        public string[] Subjects { get; set; }
    }

    public static class Student_Grading
    {
        public static Student Graded_Student(Student with_Student, string[] with_Studied_Subjects, string[] with_Grades)
        {
            if (with_Studied_Subjects.Length == with_Grades.Length)
            {
                with_Student.Grades = with_Grades;
                with_Student.Subjects = with_Studied_Subjects;
                return with_Student;
            }
            else
            {
                throw new ArgumentOutOfRangeException("Subjects taken do not contain an equal amount of grades.");
            }
        }

        public enum Grades
        {
            A, B, C, D, E, F
        }

        public enum Subjects
        {
            Geography, Maths, English, Art, Science
        }
    }

    public static class Helper
    {
        public static Student Remove_FromArray(Student thisStudent, string[] removeSubjects)
        {
            List<string> list_OfType = new List<string>();
            if (thisStudent.Subjects.Length > removeSubjects.Length)
            {
                removeSubjects.ToList().ForEach((string unwanted_Subject) =>
                {
                    foreach (string value in thisStudent.Subjects)
                    {
                        if (unwanted_Subject != value && !list_OfType.Contains(value))
                            list_OfType.Add(value);
                    }
                });
                thisStudent.Subjects = list_OfType.ToArray();
            }
            else
            {
                throw new ArgumentException("You're trying to remove more items than your collection of items contains.");
            }
            return thisStudent;
        }
    }