CISS 100 RU Dialog Boxes from The Console Window Program

I’m stuck on a Java question and need an explanation.

5-8. Modify exercise 2-4 where miles per gallon where calculated from the console window. Now modify the program so dialog boxes are used (use all arguments). The prompt and input will be a dialog box instead of a System.out.print() and sc.nextDouble(). The output will be a dialog box instead of a System.out.println(). The input and output will all be the same, but now in dialog boxes. Save as ex58.java and submit it.

 * Exercise 2-4
 * This program will calculate miles per gallon
 * */
import java.util.Scanner;
public class ex24
{
  public static void main(String[] args)
  {
    double miles, gallons, mpg;				// declare variables
    Scanner sc = new Scanner(System.in);

    System.out.print("Enter miles:  ");		// prompt
    miles = sc.nextDouble();				// input
    System.out.print("Enter gallons:  ");
    gallons = sc.nextDouble();

    mpg = miles / gallons;					// calculate

    System.out.printf("Miles per gallon is %.1fn", mpg);  // output
  }
}