Reusing Todd Lammle's method (CCNA) here, which I used in another answer.
$/27$ bits turned on is $255.255.255.224$. Thus $256 - 224 = 32$ is the block size for the last octet. So subnet addresses follow the pattern $200.10.11.0$, $200.10.11.32$, $200.10.11.64$, $200.10.11.96$, $200.10.11.128$, $200.10.11.160$ and so on.
Thus we can easily see that the given IP address is in the $200.10.11.128$ subnet, whose last valid host address is $200.10.11.158$. (as $200.10.11.159$ is the broadcast address).