**Answer and Explanation:**

a). Step 1: Calculate the option value at expiration based upon your assumption of a 50% chance of increasing to $119 and a 50% chance of decreasing to $86.

The two possible stock prices are:

S+ = $119 and S– = $86. Therefore, since the exercise price is $85, the corresponding two possible call values are:

Cu= $34 and Cd= $1.

Step 2: Calculate the hedge ratio:

(Cu– Cd)/(uS0– dS0) = (34 – 1)/(119 – 86) = 33/33 = 1

Step 3: Form a riskless portfolio made up of one share of stock and one written calls. The cost of the riskless portfolio is:

(S0– C0) = 97 – C0

and the certain end-of-year value is $86.

Step 4: Calculate the present value of $86 with a one-year interest rate of 5%:

$86/1.05 = $81.90

Step 5: Set the value of the hedged position equal to the present value of the certain payoff:

$97 – C0= $81.90

C0 = $97 - $81.90 = $15.10

b). Step 1: Calculate the option value at expiration based upon your assumption of a 50% chance of increasing to $119 and a 50% chance of decreasing to $86.

The two possible stock prices are:

S+ = $119 and S– = $86. Therefore, since the exercise price is $115, the corresponding two possible call values are:

Cu= $4 and Cd= $0.

Step 2: Calculate the hedge ratio:

(Cu– Cd)/(uS0– dS0) = (4 – 0)/(119 – 86) = 4/33

Step 3: Form a riskless portfolio made up of four shares of stock and thirty three written calls. The cost of the riskless portfolio is:

(4S0– 33C0) = 4(97) – 33C0 = 388 - 33C0

and the certain end-of-year value is $86.

Step 4: Calculate the present value of $86 with a one-year interest rate of 5%:

$86/1.05 = $81.90

Step 5: Set the value of the hedged position equal to the present value of the certain payoff:

$388 – 33C0= $81.90

33C0 = $388 - $81.90

C0 = $306.10 / 33 = $9.28