Pre-tax cost of debt is calculated as -
Yield to maturity = [ Coupon payment + ( Face value - Price) / Number of periods ] / [ ( Face value - Price) / 2 ]
Coupon payment = 9.6 % / 2 * 1000 = $ 48
Face Value = 1000
Price = 113.5 % * $ 1000 = $ 1135
Number of periods = 20 (i.e. 10 years *2 )
Yield to maturity = [ $ 48 + ( $ 1000 - $ 1135) / 20] / [ ($ 1000 + $ 1135) /2 ]
Yield to maturity = 3.86 %
Annual yield to maturity = 3.86 % * 2 = 7.72 %