Gretchen invests $5600 in a mutual fund on January 1. On March 1, she learns that her fund balance is $4000, and she then withdraws $1500. On August 1, her fund balance is $8000, and she then deposits $1300. On the following January 1, her fund balance is $6600. What is Gretchen's dollar-weighted rate of return? (Assume simple interest and months of equal length.)