Consider the setting of Problem $18.$ You decided to look for other comparables to reduce esimation error in your cost of capital estimate. You find a second firm, Thurbinar Design, which is also engaged in a similar line of business. Thurbinar has a stock price of $$20$ per share, with $15$ million shares outstanding. It also has $$100$ million in outstanding debt, with a yield on the debt of $4\mathrm{.}5\%.$ Thurbinar's equity beta is $1\mathrm{.}00.$

a$.$ Assume Thurbinar's debt has a beta of zero. Estimate Thurbinar's unlevered beta. Use the unlevered beta and the CAPM to estimate Thurbinar's unlevered cost of capital.

b$.$ Estimate Thurbinar's equity cost of capital using the CAPM. Then assume its debt cost of capital equals its yield, and using these results, estimate Thurbinar's unlevered cost of capital.

c$.$ Explain the difference between your estimates in part $($a$)$ and part $($b$).$

d$.$ You decide to average your results in part $($a$)$ and part $($b$),$ and then average this result with your estimate from Problem $17.$ What is your estimate for the cost of capital of your firm's project?