JSFiddle - React, Tailwind, and code Playground

HTML

<table width="300">
	<tr>
		<td>Item</td>
		<td>Price</td>
		<td>Qty</td>
		<td>Total</td>
	</tr>
	<tr>
		<td>Adult</td>
		<td id="price">5</td>
		<td><input type="text" name="qty" id="qty" /></td>
		<td id="total">&pound;0.00</td>
	</tr>
</table>

<input type="submit" name="submit" value="Go" id="go" />

JavaScript

$('#go').click(function() {
    if($('#qty').val() != "" && !isNaN($('#qty').val())) {
        var Total = parseInt($('#price').html()) * parseInt($('#qty').val());
        $('#total').html("&pound;" + Total);
    } else {
        alert('something is wrong');
        return false;
    }
});