CM_PER_INCH

public class JavaBook
{
    public static void main (String[] args)
    {
        final double CM_PER_INCH = 2.54;
        double paperWidth = 8.5;
        double paperHeight = 11;
        double width = paperWidth * CM_PER_INCH;
        double height = paperHeight * CM_PER_INCH;

        System.out.println("Rozmiar kartki wynosi "+width+"cm na "+height+"cm");
    }
}