please help!

The Nolan Corporation finds it is necessary to determine its marginal cost of capital. Nolan's current capital structure calls for

$35$ percent debt, $25$ percent preferred stock, and $40$ percent common equity. Initially, common equity will be in the form of

retained earnings $(K_e)$ and then new common stock $(K_n).$ The costs of the various sources of financing are as follows: debt

$($after$-$tax$),8\mathrm{.}6$ percent; preferred stock, $8$ percent; retained earnings, $14$ percent; and new common stock, $15\mathrm{.}2$ percent.

a$.$ What is the initial weighted average cost of capital? $($Include debt, preferred stock, and common equity in the form of

retained earnings, $K_e.)$

Note: Do not round intermediate calculations. Input your answers as a percent rounded to $2$ decimal places.

b$.$ If the firm has $$16$ million in retained earnings, at what size capital structure will the firm run out of retained earnings?

Note: Enter your answer in millions of dollars $($e$.$g$.,$ $$10$ million should be entered as $"10").$

Capital structure size $(x)$c$.$ What will the marginal cost of capital be immediately after that point? $($Equity will remain at $40$ percent of the capital

structure, but will all be in the form of new common stock, $K_n.)$

Note: Do not round intermediate calculations. Input your answer as a percent rounded to $2$ decimal places.

d$.$ The $8\mathrm{.}6$ percent cost of debt referred to earlier applies only to the first $$28$ million of debt. After that, the cost of debt will be

$10\mathrm{.}2$ percent. At what size capital structure will there be a change in the cost of debt?

Note: Enter your answer in millions of dollars $($e$.$g$.,$ $$10$ million should be entered as $"10").$

Capital structure size $($Z$)$

million

e$.$ What will the marginal cost of capital be immediately after that point? $($Consider the facts in both parts $c$ and $d.)$

Note: Do not round intermediate calculations. Input your answer as a percent rounded to $2$ decimal places.