Codewars – zadania

Zadanie 1:
The code gives an error!
public static final String a = 123.toString();

Moje rozwiązanie:
public class ToString {public static final String a = (String) "123";
}

Zadanie 2:
Write function bmi that calculates body mass index (bmi = weight / height ^ 2).
if bmi <= 18.5 return "Underweight"
if bmi <= 25.0 return "Normal"
if bmi <= 30.0 return "Overweight"
if bmi > 30 return "Obese"

Moje rozwiązanie:
public class Calculate {
    public static String bmi(double weight, double height) {
        double a = weight;
        double b = height;
        double bmi = (double) (a / b);
        if (bmi <= 18.5) {
            return "Underweight";
        }
        if ((bmi <= 25.0)) {
            return "Normal";
        }
        if (bmi <= 30.0) {
            return "Overweight";
        }
        if (bmi > 30) {
            return "Obese";
        }
        return null;
    }}

Zadanie 3:
Make a simple function called greet that returns the most-famous
 "hello world!".

Moje rozwiązanie:
public class HelloWorld {
    public static String greet(){
        return "hello world!";
    }
}

Zadanie 4:
Vasya Pupkin just started learning Java and C#.
At first, he decided to write simple program
that was supposed to sum up two small numbers
(numbers and their sum fit in a byte),
but it didn't work. Vasya was too sad to find out
what is wrong. Help him to correct the mistake.

Moje rozwiązanie:
public class FirstClass {
    byte a ;
    byte b;
    public static byte sum (byte a, byte b) {
        byte c = (byte) (a + b);
        return c;
    }
}