I am making a calculator form. I need to get a text box to show if one value is larger than another.

If the value from box 1 is greater than the sum that generates into box 2, I need a text box to become visable with a warning in it. 
Question 1: Do I put the code in box 2 to make the text box pop up or in the properties for the text box?
Question 2: Why isn't this working.?

var v1 = Number(this.getField(“Box1”).valueAsString);
var v2 = Number(this.getField(“Box2”).valueAsString);
if (v1 > v2)
{
event.target.display = display.visible;
}
else
{
event.target.display = display.hidden;