title: how to merge two dataframes and sum the values of columns
body: <p>I have two dataframes</p>
  
  <pre><code>df1
  Name class value
  Sri   1     5
  Ram   2     8
  viv   3     4
  
  df2
  Name class value
  Sri   1     5
  viv   4     4
  </code></pre>
  
  <p>My desired output is,</p>
  
  <pre><code>df,
  
  Name class value
  Sri   2     10
  Ram   2     8
  viv   7     8
  </code></pre>
  
  <p>Please help, thanks in advance!</p>