How can I add a float variable with a int variable in Java?

I'm new at Java so I'm also working in some exercises. This one asks me to get a bill, get a interest, calculate the interest in that bill and then return the bill plus the interest.

Here's the code:

import java.util.Scanner;
public class BillsAndInterest{
    public static void main(String[] args){
        double bill;
        System.out.println("How mutch is the bill payment? ");
           bill = new Scanner(System.in).nextDouble();
        
        System.out.println("What's the interest in this bill in per cent?");
           double interest = new Scanner(System.in).nextDouble();
        
        double interestCalculated = interest / 100 * bill;
           System.out.println("Your interest is " + interestCalculated + " dinheiros! \n So the amount is " + bill + interestCalculated + " dinheiros!");
    }
}

So the problem is, if my bill is 100 dinheiros and the interest is 25, then bill + interest must be 125, but the code returns 100.025.0 dinheiros!

I've tried changing double interestCalculated to int interestCalculated, but I got this error:<br>
BillsAndInterest.java:15: error: incompatible types: possible lossy conversion from double to int
int interestCalculated = interest / 100 * bill;
^
1 error
<br>
Can someone please help me? Is there some specific class that I should look for help?

You should only have one Scanner. The word is "much" (not "mutch"). You can declare and initialize variables with one statement. And the total of interest for 25% is 1.25 (not 0.25) and should multiply instead of adding for the message. Like,

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!");

You can try below code.

You only need to declare scanner class object once and your calculation is correct but while printing digit instead of bill + interestCalculated try with (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!");
    }
}

It's give me below 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!

The problem is with the statement:

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

The argument to System.out.println is a bunch of literals and variables connected by + operators. In the absence of any parentheses, the + operations are simply evaluated in left-to-right order, as if the statement had been written:

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);

What you wanted, of course, was to have bill and interestCalculated added together and that sum then incorporated into the overall string result, something more like this:

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);

One way to force that order of evaluation is to add parentheses around bill + interestCalculated:

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

Another alternative is to calculate the total in a separate variable and use that variable in the string expression:

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

There's also a third option which you might like even better:

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

Read more about printf here