Display menu within another to the right

body {
  font-family: sans-serif;
  width: 1080px;
  margin: 0;
  background-image: url(img/ottralogo.jpg);
  padding: 0;
  text-align: left;
  position: relative;
  margin-right: auto;
  margin-left: auto;
  color: white;
}


/*tablas del sistema*/

table {
  font-family: Sans-Serif;
  font-size: 14px;
  margin: 0;
  left: 10%;
  width: 100%;
  text-align: left;
  border-collapse: collapse;
}

table tr:nth-child(odd) {
  background-color: #81a2ac;
  font-weight: bold;
  font-size: 14px;
}

table tr:nth-child(even) {
  background-color: #d6ecf2;
  font-weight: bold
}

th {
  font-size: 14px;
  font-weight: normal;
  padding: 8px;
  background: #b9c9fe;
  border-top: 4px solid #aabcfe;
  border-bottom: 1px solid #fff;
  color: #039;
}

td {
  padding: 8px;
  border-bottom: 1px solid #fff;
  color: #669;
  border-top: 1px solid transparent;
}

tr:hover td {
  background: #d0dafd;
  color: #339;
}

.totales {
  float: right;
  width: 20%
}

select {
  color: blue;
}

.contenedor {
  position: relative;
  width: 965px;
  height: 1000px;
  margin: 0px auto;
  text-align: center;
}

.cabecera {
  width: 965px;
  height: 150px;
}

.cuerpo {
  width: 965px;
  height: 300px;
  font-size: 20px;
}

.pie {
  width: 965px;
  height: 150px;
}

table.precios tr {
  font-size: 30px;
}

div.panel-heading {
  font-size: 16px;
  font-weight: bold;
}

table.canilla tr {
  background-color: white;
  text-align: center;
  font-size: 20px;
}

table.canilla tr:nth-child(even) {
  background-color: #d6ecf2;
  font-weight: bold;
  font-size: 20px;
}

table.canilla th {
  background-color: yellowgreen;
  color: white;
  font-size: 16px;
  text-align: center;
}

select:focus {
  border-color: blue;
}

label.titulo {
  font-family: sans-serif;
  color: blue;
}

.totales th {
  width: 50%;
}

caption {
  font-family: sans-serif;
  font-size: 14px;
  font-weight: 400;
  color: black;
  background: #d9edc2;
  border: 4px solid #b2ce96;
}


/*menu*/

.dropdownmenu ul,
.dropdownmenu li {
  margin: auto;
  padding: 0;
  width: 100%;
}

.dropdownmenu ul {
  background: gray;
  list-style: none;
  font-size: 14px;
}

.dropdownmenu li {
  float: left;
  position: relative;
  width: 20%;
}

.dropdownmenu a {
  background: #30A6E6;
  color: #FFFFFF;
  display: block;
  font: bold 12px/20px sans-serif;
  padding: 10px 25px;
  text-align: center;
  text-decoration: none;
  -webkit-transition: all .25s ease;
  -moz-transition: all .25s ease;
  -ms-transition: all .25s ease;
  -o-transition: all .25s ease;
  transition: all .25s ease;
}

.dropdownmenu li:hover a {
  background: #000000;
}

.submenu {
  opacity: 0;
  position: absolute;
  visibility: hidden;
  z-index: 1;
  width: 100%;
}

li:hover ul.submenu {
  opacity: 1;
  visibility: visible;
}

.submenu li {
  float: none;
  width: 100%;
}

.submenu a:hover {
  background: #DF4B05;
}

.submenu a {
  background-color: #000000;
}

.botonimagenrefresh {
  background-image: url('iconos/refresh.png');
  background-repeat: no-repeat;
  background-position: left;
  background-color: grey;
  font: sans-serif;
  border: 0px;
}

div {
  margin: auto;
  width: 100%;
}

h3 {
  font: sans-serif;
}

<div class="row">
  <nav class="dropdownmenu">
    <ul>
      <li><a href="">ABM</a>
        <ul class="submenu" id="a">
          <li><a href="index.php?controller=cliente&action=index">Clientes</a></li>
          <li><a href="index.php?controller=articulo&action=index">Articulos</a></li>
          <li><a href="index.php?controller=proveedor&action=index">Proveedores</a></li>
          <li><a href="index.php?controller=envase&action=todos">Envases</a></li>
          <li><a href="index.php?controller=medida&action=index">Medidas</a></li>
          <li><a href="index.php?controller=canilla&action=index">Canillas</a></li>
          <li><a href="index.php?controller=user&action=index">Usuarios</a></li>
        </ul>
      </li>
      <li><a href="">Nuevo comprobante</a>
        <ul class="submenu" id="b">
          <li><a href="index.php?controller=ticket&action=index">Ticket</a></li>
          <li><a href="index.php?controller=facturaa&action=index">Factura</a></li>
        </ul>
      </li>