jQuery does not calculate Value Added Tax on Form

I have added this field to my form in order to calculate value added tax (vat):

<div class="col-md-4">
    <div class="form-check">
        <input type="radio" id="vat_on" name="vat" value="on" checked>
        <label class="form-check-label">
        Calculate value added tax  
        </label>
    </div>
    <div class="form-check">
        <input type="radio" id="vat_off" name="vat" value="off">
        <label class="form-check-label">
            Do not calculate value added tax
        </label>
    </div>
</div>

And I tried adding this as jQuery:

if($('[name=vat]:checked').val() === 'on'){
   var value_added_tax = ((price_final*cnt) - ((price_final*cnt)*0.9)).toLocaleString();
}else{
   var value_added_tax = (0).toLocaleString();
}

But when I test this and checked the Calculate value added tax radio button, it returns: Nan !

However it should be returning a value instead of Nan.

I have also tried removing toLocaleString() from both conditions, but didn't solve the problem.

So what is going wrong here ? How can I fix this issue ?

I would really appreciate any idea or suggestion from you guys...

Thanks in advance.

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