JSFiddle - React, Tailwind, and code Playground

HTML

<form>
<input id="quantity" class="qty" type="text" placeholder="quantity" />
</form>

<!--display total cost here--> 
<span>The Cost is: totalcost</span>

JavaScript

var cost = 25;

/*function(updater) {
    var cost = 25;
    var quantity = receive quantity from the form input
    var totalcost = (cost * quantity);
    
    send total back to html document and display as total cost
    
*/