JSFiddle - React, Tailwind, and code Playground

HTML

<select id="SendingType">
    <option value='2'>Normal</option>
    <option value='0'>Express</option>
</select>
<button id="calculate">calculate</button>
<div id="result" />

JavaScript

$(function () {
    $("#calculate").click(function () {
        var result = $("#SendingType").val();
        var day1 = eval(result) + 3;
        var day2 = eval(result) + 10;
        var day3 = eval(result) + 2;
        if ($("#SendingType").val(2)) {
            $("#result").text(day1 + " and " + day2 + " days.");
        } else {
            $("#result").text(day1 + " and " + day3 + " days.");
        }
    });
});