title: Oracle SQL: Adding hours to a date
body: <p>Starting with the date/time of July 20, 2001 10:40:12, display the following result table. Use the Dual table.</p>
  
  <ul>
  <li><p>subtract 2 days<br>
  Result :18-jul-01 10:40:12</p></li>
  <li><p>add half a day<br>
  Result: 20-jul-01 22:40:12</p></li>
  <li><p>add 4and half hours<br>
  Result: 20-jul-01 15:10:12</p></li>
  </ul>