Donald invested $1,000 in large U.S. stocks at the beginning of 2012. This investment earned 17.45 percent in 2012, 33.85 percent in 2013, 11.00 percent in 2014, and 2.00 percent in 2015. What was the average annual return that Donald earned over the 20122015 period. (Round answer to 2 decimal places, e.g. 1.52.)