$n=k+m=11+4=15$. where $n$ is the length of the codeword. $k$ is the length of the message and $m$ is the length of the parity bits. For hamming code, $2^{m} = k+m+1$ , here $k\geq 11$ , So, $2^{m} -m-1 \geq 11$ , So, $m=4$. Since, $n$ is defined as $k+m$. So, it will be $11+4=15$