JSFiddle - React, Tailwind, and code Playground

HTML

<select id="sizeBoxSelect">
    <option selected>Please Select</option>
    <option>HP to decide</option>
    <option value="45,40" >45x40</option>
    <option value="50,20" >50x20</option>
    <option value="50,30" >50x30</option>
    <option value="63,30" >63x30</option>
    <option value="75,40" >75x40</option>
</select>
<div id="sizeBox" style="border:2px solid"></div>

JavaScript

$(function () {
    $(document).on("change", "#sizeBoxSelect", function () {
        var $this = $('select#sizeBoxSelect option:selected'),
            iWidth = parseInt($this.val().split(",")[0]),
            iHeight = parseInt($this.val().split(",")[1]);
        
        $("#sizeBox").width(iWidth).height(iHeight);
    });
});