Shadow Corp. has no debt but can borrow at $5\mathrm{.}75$ percent. The firm$$s WACC is

currently $8\mathrm{.}9$ percent, and the tax rate is $22$ percent.

a$.$ What is the firm$$s cost of equity?

b$.$ If the firm converts to $25$ percent debt, what will its cost of equity be$?$

c$.$ If the firm converts to $50$ percent debt, what will its cost of equity be$?$

d$.$ What is the firm$$s WACC in part $($b$)?$ In part $($c$)?$