[["", "2018", "2017", "2016"], ["balance at beginning of year", "$ 38.9", "$ 44.0", "$ 46.7"], ["additions charged to expense", "34.8", "30.6", "20.4"], ["accounts written-off", "( 39.4 )", "( 35.7 )", "( 23.1 )"], ["balance at end of year", "$ 34.3", "$ 38.9", "$ 44.0"]]