Your firm recently paid a dividend of $4 to common stockholders. Dividends are expected to grow at 8% per year for the foreseeable future. The current stock price is $54. New shares could be sold for the same price, but flotation costs would amount to $6 per share.

A $15 million bank line of credit is available with an interest rate of 9%. The firm's tax rate is 34%.

What is the firms cost of capital if their capital structure consists of 60% external equity and 40% bank loans?

the answer is 12.58% but need to know how to work this question out