I built $a15-$period binomial model whos parameters are calibraated $to$ black scholes geomeatric brownian motion with $T=0\mathrm{.}25$ years, $S=100,r=2\%,pi=30\%anda$ divident yield $ofC=1\%,u=1\mathrm{.}0395,$ computed the price $ofan$ american call option with strike $K=110$ and maturioty$=0\mathrm{.}25$ years and the answer $is2\mathrm{.}61.$ Then I calculated the price $ofan$ American put option with strike $K=110an$ dmaturity $=0\mathrm{.}25$ years which $is12\mathrm{.}36.$ There $asan$ option $to$ optimal $to$ early exerstio $to$ put option #$2.$ Now, the question $is,$ because $we$ answered yes $to$ the early option, when $is$ the earliest period $at$ which $it$ might $be$ optimal $to$ early exercise? round $to$ the second decimal place