How to get starting and ending date of a week based on" week of month "selection

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Javascript

PHP

How can i achieve the following using php

Based on week selection(1,2,3,4) of a month

1st Week: start- 5th Jan, 2012. End-12th Jan, 2012

2nd Week: 12th Jan, 2012. End- 19th Jan, 2012.

3rd Date: 19th Jan, 2012. End- 26th Jan, 2012.

4th week: 26th Jan, 2012. End- 02 Feb, 2012.