The price of an American put with the maturity of 6 months on a non-dividend-paying stock is $3. The stock price is $29, the strike price is $28. The risk-free interest rate is 8%. What is the product(multiplication) of the upper and lower bounds for the price of an American put on the same stock with the same strike price and expiration date.

a. $1.80

b. $2.23

c. $2.80

d. $1.23