问题在于声明：

System.out.println("Your interest is " + interestCalculated + 
   " dinheiros! \n So the amount is " + 
   bill + interestCalculated + " dinheiros!");

对…的论点 System.out.println 是一组文字和变量通过 + 操作员。如果没有任何括号，则 + 操作只是按照从左到右的顺序进行计算，就好像语句是这样写的：

String $T1 = "Your interest is " + interestCalculated;
String $T2 = $T1 + " dinheiros! \n So the amount is ";
String $T3 = $T2 + bill;                   // String + number = String
String $T4 = $T3 + interestCalculated;     // String + number = String
String $T5 = $T4 + " dinheiros!";
System.out.println($T5);

当然，你想要的是 bill 以及 interestCalculated 加在一起，然后将总和合并到整个字符串结果中，类似于：

String $T1 = "Your interest is " + interestCalculated;
String $T2 = $T1 + " dinheiros! \n So the amount is ";
double $T3 = bill + interestCalculated;     // number + number = number
String $T4 = $T2 + $T3;                     // String + number = String
String $T5 = $T4 + " dinheiros!";
System.out.println($T5);

强制这种求值顺序的一种方法是在其前后加上括号 bill + interestCalculated :

System.out.println("Your interest is " + interestCalculated + " dinheiros! \n So the amount is " + (bill + interestCalculated) + " dinheiros!");

另一种方法是在单独的变量中计算总数，并在字符串表达式中使用该变量：

double totalAmount = bill + interestCalculated;
System.out.println("Your interest is " + interestCalculated + " dinheiros! \n So the amount is " + totalAmount + " dinheiros!");

还有第三种选择，你可能更喜欢：

System.out.printf(
    "Your interest is %.2f dinheiros! %n So the amount is %.2f dineheiros!%n", 
    interestCalculated, 
    bill + interestCalculated);

阅读更多关于 printf 在这里

你应该只有一个 Scanner . 这个词是“much”（不是“mutch”）。可以用一条语句声明和初始化变量。25%的利息总额是 1.25 （不是 0.25 )消息应该是乘法而不是加法。比如，

Scanner scan = new Scanner(System.in);
System.out.println("How much is the bill payment? ");
double bill = scan.nextDouble();

System.out.println("What's the interest in this bill in per cent?");
double interest = 1 + (scan.nextDouble() / 100);

double interestCalculated = interest * bill;
System.out.println("Your interest is " + interestCalculated 
        + " dinheiros!\nSo the amount is " + bill
        + " + " + interest + "% dinheiros!");

你可以试试下面的代码。
您只需要声明scanner类对象一次，并且您的计算是正确的，但是在打印数字而不是 bill + interestCalculated 尝试 (bill + interestCalculated) ```
class BillsAndInterest{
public static void main(String[] args){
double bill;
Scanner scanner=new Scanner(System.in);
System.out.println("How mutch is the bill payment? ");
bill = scanner.nextDouble();

    System.out.println("What's the interest in this bill in per cent?");
    double interest = scanner.nextDouble();

    double interestCalculated = interest / 100 * bill;
    System.out.println("Your interest is " + interestCalculated + " dinheiros! \n So the amount is " + (bill + interestCalculated) + " dinheiros!");
}

}

### 这是给我低于o/p

How mutch is the bill payment?
100
What's the interest in this bill in per cent?
25
Your interest is 25.0 dinheiros!
So the amount is 125.0 dinheiros!