JSFiddle - React, Tailwind, and code Playground

HTML

<div>Qty:	<span class='minus' class="signrm">&mdash;</span> 
    <input type="text" name="qty" class="txt qty" value="1" /> <span class='plus'>+</span>

    <br/>Price:
    <input type="text" name="price" class="txt price" value="500" />
    <br/>Total:
    <input type="text" name="total" class="txt total" value="500" />
</div>

JavaScript

$(function () {
    $('.minus, .plus').click(function () {
        var $qty = $(this).siblings('.qty');
        var qtyCounter = parseInt($qty.val());
        if($(this).hasClass('plus'))
            qtyCounter++;
        else
            qtyCounter--;
        $qty.val(qtyCounter);
        var pricePerUnit = $(this).siblings('.price').val();
        var quantity = $(this).siblings('.qty').val();
        var total = quantity * pricePerUnit;
        $(this).siblings('.total').val(total);
    });
});