Discount Assignment: If/Else Statement

Its an assignment that I've spent hours on:

http://imageshack.us/a/img834/7124/273e.png

http://imageshack.us/a/img706/4691/fhfd.png

That's how far I've gotten so far, next up is my code:

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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 yourPurchase:String;

var yourDiscount:String;

var yourPrice:String;

var discount:Number;

var total:Number;

yourPurchase = max_txt.text;

discount: 10.00 / 10%

yourDiscount = discount_txt.text;

yourPrice = price_txt.text;

total = yourPurchase - discount

if(yourDiscount)

{

      trace();

}

else

{

     trace();

}

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As you can see, I have no clue on how to get the discount written in code, I don't know how.

Please explain as best as you can about how to solve this dilemma (in Laymen's Terms if possible). Thank you!