Formula to calculate days in month Item is Held

Hi,

In the attached file, in the area highlighted in yellow, I need help trying to figure out how to populate in each month, how many days a item will be held until sold. There is a purchase date and a sale date referenced. This will calculate how many days the item is held.

I'm trying to figure out how many days it will be held in month 1, month 2, month 3 etc. I've filled in the cells manually for purposes of example.

Thanks in advance.

-Manny