Gul buys a 7.4% coupon bond with $1,000 face value and 9.3% yield to maturity. The bond makes semi-annual coupon payments and has 20 years to maturity. The yield to maturity of this bond increases to 10.3% six months later. Calculate Gul's return on investment over the 6-month period.

(Intermediate computations should not be rounded. Enter your result as a percentage with two decimal places rounded off. A minus symbol should be used to denote a negative value.)