您需要计算3小时的价格，并从第二种情况下的总小时数中扣除。同时对原始价格进行折扣，将其乘以剩余工时，再将这些工时价格加上3小时价格。
代码如下

import java.util.Formatter;
import java.util.Scanner;
public class string{
public static void main(String[] args){

    double bill= 0;
    Scanner scan = new Scanner(System.in);

    System.out.print("ENTER REGULAR CHARGE: ");
    double charge = scan.nextInt();

    System.out.print("ENTER REGULAR HOURS: ");
    int hours = scan.nextInt();

    scan.close();

    if (hours <= 3){
        // calculation for 3 hours or less
        bill= charge * hours;
        System.out.print("RENTAL BILL IS: " +bill);
    }
    else {
        // subtracting 3 hours from total hours if hours are more                              
        int remainingHrs = hours - 3; 

        // calculating price for 3 hours to add to remaining hours price                                         
        double priceforthreeHours = charge * 3;

        // calculating discountedprice (10% discount)
        double discprice = charge - (charge * 0.10);

        // adding it all together 3hrs + discounted price                                                        
        bill = priceforthreeHours +(remainingHrs * discprice);

        System.out.print("RENTAL BILL IS: ");

        // formatting price using java.util.Formater
        System.out.printf(" %.2f, %n",bill); 

    }
}

}