My granddaughter has a college class and they use xml spreadsheets with formulas. How does she convert these files to a format that libre office can work with?

**Update 2019-05-09T18:55+02:00** (erAck: moved the following section from *Answer* to this *Question*)

The spreadsheet was created with Exxel. My granddaughter uses Libre Office Calc. When she opens the .xml spreadsheet, she gets errors in the cells that have formulas. In the formula composition line above, the formulas have an =of in front of the normal formula. If I go to each individual cell that contains a formula and delete that prefix, it works for multiplication functions. But for formulas that output an average of the numbers in three cells, it still does not work.Here is one of her files.link text