Gretchen invests 6200 dollars in a mutual fund on January 1. On March 1, she learns that her fund balance is 3800 dollars, and she then withdraws 1500 dollars. On August 1, her fund balance is 7800 dollars, and she then deposits 1100 dollars. On the following January 1, her fund balance is 7900 dollars. What is Gretchen's dollar-weighted rate of return? (Assume simple interest and months of equal length