JSFiddle - React, Tailwind, and code Playground

HTML

<select id="selectBox">
<option selected>Please Select</option>
<option>HP to decide</option>
<option>45x40</option>
<option>50x20</option>
<option>50x30</option>
<option>63x30</option>
<option>75x40</option>
</select>
<div id="sizeBox"></div>

CSS

#sizeBox {
    background:blue;
}

JavaScript

$('#selectBox').change(function() {
    $("option:selected", this).each(function () {
        var value = $(this).val();
        var height = value.split('x')[0];
        var width = value.split('x')[1];
        $('#sizeBox').css("width", width);
        $('#sizeBox').css("height", height);
    });
});