JSFiddle - React, Tailwind, and code Playground

HTML

Drop Value:
<input type="checkbox" name="drop" />
<ul id="items">
    <li class="itemadd">Item 1</li>
    <li class="itemadd">Item 2</li>
    <li class="itemadd">Item 3</li>
</ul>
<br />
<button id="addCalc">Add Item And Calculate</button>
<br />
<button id="calc">Calculate</button>
<br />
<div id="dropPrice">0</div>

JavaScript

var dropResult;
$(function () {
    $("#calc").on('click', function () {
        $('#dropPrice').text( '$' + (450 + ((450 * ($('#items .itemadd').length - 1)) / 3)) / (Number($("input[name=drop]").is(':checked')) + 1));
    });
    
    $('#addCalc').on('click', function(){
        $('#items').append('<li class="itemadd">Item '+ ($('#items .itemadd').length + 1) +'<l/i>');
        $("#calc").trigger('click');
    });
});