Eight years ago WFF Corporation issued bonds with a total face value of $10 million. One bond has a face value of $500,000. The bonds have a coupon rate of 8% p.a. and coupons are paid annually. The bonds mature in six years from today. The bonds currently yield 6% p.a. WFF Corporation has 8 million ordinary shares outstanding that are currently priced at $17 each and have a beta of 0.70. The company has 1,000,000 preference shares trading at $12 each. The return on the stock market is 16% p.a., the risk-free return is 1% p.a., and the company tax rate is 30%.

What proportion of the firm's capital structure is debt?