Wendel invests 6600 dollars in a mutual fund on January 1. On June 1, his fund balance is 3800 dollars. Wendel notices the decline, and withdraws 1500 dollars. On September 1, his fund balance is 7800 dollars, and he then invests an additional 1400 dollars. On the following January 1, his fund balance is 6400 dollars. What is Wendel's time-weighted rate of return?