Complex sentence: At the start of 2007, the company had an average of 338 employees for each Walmart and Sam's Club store in the United States, and by April 2013, this had reduced to an average of 281 employees per store.
Split into simpler sentences: At the start of 2007, the company had an average of 338 employees for each Walmart and Sam's Club store in the United States. By April 2013, this had reduced to an average of 281 employees per store.