If the following methods are declared in a class, which of them fail to compile because of overloading rules?

public static int f$2($int a$,$ int b$)//1$

public static double f$2($double a$,$ int b$)//2$

public static double f$2($int a$,$ double b$)//3$

public static void f$2($double a$)//4$

public static int f$2($int a$)//5$

public static void f$2($int a$)//6$