public static string GetRespondentNumber(User user)
{
QuizzyContext db = new QuizzyContext();
string nextNumber = GetNextRespondentNumber(user.LastRespondentNumber);
user.LastRespondentNumber = nextNumber;
db.Entry(user).State = System.Data.Entity.EntityState.Modified;
db.SaveChanges();
return($"A{nextNumber[0]}B{nextNumber[1]}C{nextNumber[2]}D{nextNumber[3]}");
}