Object-Oriented Programming (Using Java Language) =

import java.util.Scanner;

class Main {  

 public static void main(String args[]) {

       Scanner scan = new Scanner(System.in);

       System.out.print("Enter a decimal value (0 to 15): ");

       int num = scan.nextInt();

       scan.close();

       if (num < 0 || num >15) {

           System.out.printf("%d is an invalid input\n", num);

       } else {

           System.out.printf("The hex value is %X\n", num);

       }

 }

}

Explanation:

Hopefully this example will get you going for the other assignments.

its tabs i just searched it up so try tabs