Help with Weight Calculator (Metric and Imperial)

http://imageshack.us/a/img59/6380/qeup.png

http://imageshack.us/a/img203/7864/9zur.png

So, long story short, here is what I've learned to use so far: if/else statements, while/for loops, and counters. I need to create a Weight Calculator that allows me to choose to enter in Metric or Imperial IBM. I also need to determine the Height in metres or inches. Regardless, I am stumped; I do not know how to start the program let alone complete it. This is the code I have so far:

"var body_txt:TextField = new TextField();

body_txt.x = 225;

body_txt.y = 300;

body_txt.autoSize = TextFieldAutoSize.LEFT;

var myFormat:TextFormat= new TextFormat();

var yourName:String;

var yourSystem:String;

var yourHeight:String;

var total:Number;

yourName = name_txt.text;

yourSystem = system_txt.text;

yourHeight = height_txt.text;

blue_btn.addEventListener(MouseEvent.CLICK, onClick);

function onClick(event:MouseEvent):void {

addChild(body_txt);

body_txt.text= ""+ yourName +"'s ideal weight will be"

}"

I was thinking about starting with an "if statement" but I think there can be many other possibilities.