function recalculate_item(amount) {
    var item_name = $('input#my_item_name').val();
    var item_price = $('input#my_amount').val();
    //set new visible price
    $('span#new_amount').html(amount * item_price);
    //set paypal price
    $('input#paypal_amount').val(amount * item_price);
    //set paypal name
    $('input#paypal_item_name').val(amount + ' Case of ' + item_name);    
}

$(window).ready(function(){    
    $('input#over21').click(function(){
        if (this.checked == true) {
            $('input#addtocartbutton').attr({disabled: ''});
        } else {
            $('input#addtocartbutton').attr({disabled: 'disabled'});
        }
        });
});