Welcome to the Ranch
If you are not experienced in GUIs, you will find the automated GUI builders make the code harder for you to understand. Do you have an application which converts km to miles and
vice versa? If not, you will find things difficult. You need an application which you can pass km to and get miles or
vice versa. Then you consider putting a GUI around that application.
Miles is km / 1.6 not km * 1.6. Well, actually, 1.609344.
Put [code=java] before the code and [/code] after it. More details
here. I have corrected it for you