My 2nd problem

Answer 1

refering you to a similar post with some deep explanation from me:
https://www.sololearn.com/Discuss/1248715/?ref=app

Answer 2

Consider a student registration program used by the registrar’s office. The program keeps track of students who are registered for a given semester. For each student registered, the program maintains the student’s name, address, and phone number; the number of classes in which the student is enrolled; and the student’s total credit hours. The program also keeps track of the total number of registered students. Define a Student class that is suitable for this program and develop an application that can accomplish the above mentioned tasks