计算数据表中一组记录的首次登录和上次注销之间的持续时间

I am reading an Excel document using ADO.Net into a Dataset. Dataset Contains set of employee records which contains login and logout time as a Datatable. I need to fetch the employees's first login and last logout time as final record from the set of records based on employee id and date. Here is my example data:I am reading an Excel document using ADO.Net in