A stock index is currently 1,500. Its volatility is $18 \%$. The risk-free rate is $4 \%$ per annum (continuously compounded) for all maturities and the dividend yield on the index is $2.5 \%$. Calculate values for $u, d$, and $p$ when a 6 -month time step is used. What is the value a 12 -month American put option with a strike price of 1,480 given by a two-step binomial tree.