JSFiddle - React, Tailwind, and code Playground

HTML

<form id="form" name="form" method="post">
  <a href="#" onclick="AgregarCampos();">Agregar Nota</a>
  <ul id="campos"></ul>
  <fieldset>
    <label for="promedio">Su promedio es:</label>
    <input type="number" name="promedio" id="promediof" step="any">
  </fieldset>
  <a href="#" onclick="resetear();">Limpiar formulario</a>
</form>

JavaScript

var nextinput = 0;
var total = 0;

function AgregarCampos() {
  nextinput++;
  campo = '<li id="idLi' + nextinput + '"><input type="number" size="20" id="nota' + nextinput + '" name="nota' + nextinput + '" step="any" onChange="multiplicar(\'nota' + nextinput + '\',\'pondera' + nextinput + '\',\'acumu' + nextinput + '\');" value=0 /> x <input type="number" size="20" id="pondera' + nextinput + '" name="pondera' + nextinput + '" step="any" onChange="multiplicar(\'nota' + nextinput + '\',\'pondera' + nextinput + '\',\'acumu' + nextinput + '\');" value=0 /> = <input type="number" size="20" id="acumu' + nextinput + '" name="acumu' + nextinput + '" step="any"/></li>';
  $("#campos").prepend(campo);
}

function resetear() {
	$('#campos > li').remove();
  $('#form')[0].reset();
}

function multiplicar(nota, pondera, acumu) {
  m1 = document.getElementById(nota).value;
  m2 = document.getElementById(pondera).value;
  r = m1 * (m2 / 100);
  total = total + r;
  document.getElementById(acumu).value = r;
  document.getElementById("promediof").value = total;
}