Clearwater Ltd$.$ has determined its optimal capital structure, which comprises the following:

FORM OF CAPITAL WEIGHT AFTER$-$TAX COST

Long$-$term debt $70\%4\%$

Preference shares $20\%13\%$

Ordinary shares $10\%10\%$

The weighted average cost of capital is $...$

a$.$

$9\mathrm{.}1\%$

b$.$

$8\mathrm{.}4\%$

c$.$

$6\mathrm{.}4\%$

d$.$

$5\mathrm{.}3\%$