title: How to sum grid column in extjs4.1
body: <p>I have the grid like below. Can anybody tell me how to sum all the grid columns and display  them in the grid row</p>
  
  <p>e.g</p>
  
  <pre><code>      Month   Achieve Target 
  
        Jan     3000     4000
        Feb     2000     5000
  
     **Total    5000     9000**   need to add total row in grid
  </code></pre>
  
  <p>Thanks</p>