find End date based on Start date and number of weeks C#.net

Question

hi friends,

 

I am using gridview in that I have one bound field and 3 textbox template fields like this

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phase      Duration(weeks)    SrartDate         EndDate 

 

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out side of gridview I have field: working days in a week: 

ex: 5 0r 6 

 

If I enter 1 or 1.5 in Duration textbox , start Date : 12-05-2017 and if total working days in a week: 5  based on this values remove sturdays and sundays and find and display

 End Date in gridview.

 

if working days in a week 6 days remove only sundays and find EndDate and display it in gridview.

 

how to achive this??