title: how to calculate(sum up) an a row value of an datatable
body: <p>i have an datatable like this.
  i am getting this  data  from an excel sheet and  converted  to  datatable</p>
  
  <pre><code>id  workedhours  tfshours
  1     3          2
  2     5          5
  3     .7         3
  4      2         3.2
  5     4.3       6.8 
  </code></pre>
  
  <p>now i need  the  sum  of the column workedhours and  tfshours</p>
  
  <p>how can i achive that is .there any builtin  function to get the sum of teh  column </p>
  
  <p>i need  the  result like  this  in  a  new  datatable</p>
  
  <pre><code> workedhours   tfshours
  15                20
  </code></pre>
  
  <p>any help  would  be  greatly appreicated.
   thank you </p>