The following information relates to DTF Corporation. Eight years ago the company issued bonds with a total face value of $$7$ million. One bond has a face value of $$100,000.$ The bonds have a coupon rate of $4\%$ p$.$a$.$ and coupons are paid semi$-$annually. The bonds mature in seven years from today. DTF Corporation has $5$ million ordinary shares outstanding that are currently priced at $$4$ each and have a beta of $0\mathrm{.}8.$ The bonds currently yield $5\%$ p$.$a$.,$ the return on the stock market is $8\%$ p$.$a$.,$ the risk$-$free return is $2\%$ p$.$a$.,$ and the company tax rate is $30\%.$ The company has $600,000$ preference shares trading at $$5$ each.

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

$[$Where applicable, show as much working out as possible, otherwise you may be penalised$].$