you are trying to analyze the optimal debt ratio for britannia hotels, a firm that owns and opertates a number of small hotels. the firm has 50 million shares trading at 10 dollar a share and 125 dollar in debt outstanding. The current levered beta for firm is 0.90 and pre-tax cost of borrowing is 7%. the risk free rate is 5%and the market risk premium is 4%(corporate tax rate is 40%)

1 estimate the current cost of capital for britannia hotels
2 the firm is planning to triple its dollar debts and use the proceeds to buy back stock, if it does so, it believes that its pre-tax cost of borrowing will rise to 8%. Estimate the cost of capital for britannia hotels, if it does this
3 if you were told that investor in britannia hotels were rational an that the stock price increased by 1.5 dollar per share on the announcement of buyback, estmate the expected growth rate in annual savings that market must be assuming
大家告诉我，解题的思路和要用到的公式就好了，尤其是第三问；谢谢了哦！