3. In Chapter 8, you can find how to calculate call and put option price by using Black-Scholes option pricing model.

a) Create your own function to calculate put option price. That is, you have to complete the body of the following function (S0: current stock price, K: strike price, r: risk-free rate, T: remaining time to maturity, and sigma: standard deviation of underlying stock price).

 put <- function (S0, K, r, T, sigma) {

 COMPLETE THIS PART

}

b) Using your own function created in part a), calculate put option price with

S0 = $1,000

K = $850

r = 3%

T = 3 years

sigma = 23%