6 Month Average

Hello,

I am trying to create a report that calculates the average amount of hours an employee has worked in a 6 month timeframe. Ultimately, I am looking for help creating the formula that will calculate 6 months back from the date I enter in my parameter and find the average hours worked within the time frame. I do not want to have to enter in the 6 month date in addition to the original calculation date.

Any help would be greatly appreciated. Thank you.