SOURCE

<div class="container">
    <div class="top">top</div>
    <div class="bottom">
      <div class="left">left</div>
      <div class="right">right</div>
    </div>
  </div>

.container{
  height:500px;
  width:100%;
  border:1px solid;
}
.top{
  border:1px solid;
  height:80px; 
  float:left;
  width:100%;
}
.bottom{
  height:calc(500px - 84px);
}
.left{
  border:1px solid;
  width:120px;
  float:left;
  height:calc(500px - 84px);
}
.right{
  border:1px solid;
  float:left;
  width:calc(100% - 124px);
  height:calc(500px - 84px);
}