7. (6 points) A call option is the right to buy stock at $25 a share. According to the Black/Scholes option valuation model, what is the value of the call a. if the price of the stock is $25, the interest rate is 8 percent, the option expires in three months, and the standard deviation of the stock's return is 0.20 (20 percent)? $1.25 b. if the price of the stock is $25, the interest rate is 6 percent, the option expires in three months, and the standard deviation of the stock's return is 0.20 (20 percent)? c. if the price of the stock is $27, the interest rate is 8 percent, the option expires in three months, and the standard deviation of the stock's return is 0.20 (20 percent)