13. A firm's common stock is currently selling for $20 per share. The dividend expected to be paid at the end of the coming year is $1.80. Its dividend payments have been growing at a constant rate for the last four years. Four years ago, the dividend was $1.50. What is the firm's cost of its common stock? If you could please work this in excel and show which formulas are used, that would be awesome. Thank you.