Please help me answer this in excel: The current price of a stock is $$50,$ and the annual risk$-$free rate is $5\mathrm{.}5\%.$ A call option with a strike price of $$43$ and with $1$ year until expiration has a current value of $$13\mathrm{.}78.$ What is the value of a put option written on the stock with the same exercise price and expiration date as the call option?