Custom calculation

[defaultbs5znr1ycsus]

Hi, I would like to add a custm calculation in my tax box. 

I want the user to check off either of the following: 

No tax

13% tax

15% tax

Once checked, I want the percentage amount to calculate with the subtal.

What would be my script?

[Nesa Nurani]

As custom calculation of tax field use this:

var notax = this.getField("taxnone").value;
var t13 = this.getField("tax13").value;
var t15 = this.getField("tax15").value;
var sub = Number(this.getField("subtotal").value);
if(notax != "Off")
event.value = 0;
else if(t13 != "Off")
event.value = .13*sub;
else if(t15 != "Off")
event.value = .15*sub;
else event.value = "";

Check if field names are correct, if not, change them to your actual field names.

[defaultbs5znr1ycsus]

Thank you very much for your time!!!