Shouldn't users be allowed to delete their answers in

[i accidentally gave wrong answer and now i want to delete it or edit it. but i can't because it won't allow me to.]

abstract class Mark  //Creating an Abstract class{

abstract double getPercentage();}

class A extends Mark{

double result;

A( int val1, int val2, int val3){

 result=(val1+val2+val3)/3;}

double getPercentage(){

 return result;}}

class B extends Mark{

double result;

B(int val1, int val2, int val3, int val4){

 result=(val1+val2+val3+val4)/4;}

double getPercentage(){

 return result;}}

class Main{

public static void main(String args[]){

 //class A Object

 Mark obj_1=new A(10,20,30);

 System.out.println(obj_1.getPercentage());

 //class B Object

 Mark obj_2=new B(10,20,38,46);

 System.out.println(obj_2.getPercentage());}}