The following information relates to OMG Corporation. Eight years ago the company issued bonds with a total face value of $7.5 million. One bond has a face value of $500,000. The bonds have a coupon rate of 6% p.a. and coupons are paid annually. The bonds mature in six years from today. OMG Corporation has 6 million ordinary shares outstanding that are currently priced at $12 each and have a beta of 0.90. The bonds currently yield 4% p.a., the return on the stock market is 12% p.a., the risk-free return is 1.5% p.a., and the company tax rate is 30%. The company has 1,250,000 preference shares trading at $9 each.

What proportion of the firm's capital structure is preference shares?