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

FORM OF CAPITAL WEIGHT AFTER$-$TAX COST

Long$-$term debt $60\%5\%$

Preference shares $15\%13\%$

Ordinary shares $25\%10\%$

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

a$.$

$7\mathrm{.}45\%$

b$.$

$11\mathrm{.}43\%$

c$.$

$8\mathrm{.}35\%$

d$.$

$9\mathrm{.}65\%$