JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div class="qty">
		  <input type="text" name="quantidade" maxlength="3" />
		  <input type="text" name="valor_unitario" />
      <input type="text" name="vaor_total" />
</div>
<div class="qty">
		  <input type="text" name="quantidade" maxlength="3" />
		  <input type="text" name="valor_unitario" />
      <input type="text" name="vaor_total" />
</div>
<input type="button" id="btCalcular" value="Calcular"/>

JavaScript

$('#btCalcular').click( function () {
	 $('.qty').each(function () {
     console.log(this);
   		var qtd = $(this).find('input[name=quantidade]').val()
      var val = $(this).find('input[name=valor_unitario]').val();
      var total = parseFloat(qtd) * parseFloat(val);
      $(this).find('input[name=vaor_total]').val(total);
   });
})