You can create a formula that will do this by using an IF function to check whether the value is negative and then multiplying the value by -1 if it is.
Your IF formula will look something like:
If you're having trouble understanding this formula, you can find more explanation of the IF function in Expert Skills Lesson 3-5: Use the IF logic function.
I have attached a copy of your spreadsheet with the formula applied.
I hope this is helpful. Feel free to reply if you need any more assistance.
Jonathan is part of the professional team who answer Excel-related questions posted on the ExcelCentral.com forums.
Jonathan also tests our courses prior to publication and has worked on all of our six world best selling Excel books and over 850 video lessons for Excel 2007, Excel 2010 and Excel 2013.
As well as extensive Excel knowledge, Jonathan has worked in the IT world for over thirteen years as a programmer, database designer and analyst for some of the world's largest companies.