How I solve it?

Quantitative Problem: 5 years ago, Barton Industries issued 25-year noncallable, semiannual bonds with a $1,000 face value and an 8% coupon, semiannual payment ($40 payment every 6 months). The bonds currently sell for $847.87. If the firm's marginal tax rate is 25%, what is the firm's after-tax cost of debt? Do not round intermediate calculations. Round your answer to two decimal places. %