How to Calculate Date Differnce in days, weeks or months

The problem is that your dates are not numbers, they are text. The date dif formula works with numbers (formatted as dates).
try to use find and replace, find what >> , (comma) and replace with >> leave blank.

There are 2 problems, the dates are not only text, but the dates are also formatted: m/d/yyyy, but in England if date is in text, Excel expects format dd/mm/yyyy (or d/m/yyyy).
So first you should switch the date and the month in the string before you can convert the string to a date.

And the formula for this is in Excel 2010 more difficult, because you have to figure out exactly where the day and year start. After all, the month can take up 1 or 2 positions and perhaps the day of the month too. That is more difficult in Excel 2010 than in Office 365.

Are you still using Excel 2010?

OK, then you've already solved a lot yourself.

I'll tried your formula and it returns 10 week(s) and 6 day(s)

Are there any questions left?

Would you also like to update your MS-Off version in your profile?
Otherwise you will not be presented with the formulas that best suit your current version.

The differences between the different MS-Off versions are very large.