Interior and exterior of a subset in the relative topology of the ambient space Let $X = (0, 4] \cup \{ 6 \} \cup [10, 11] \subset \Bbb R$. How do I find the interior and exterior of $A = (0, 2] \cup \{ 6 \} \cup (10, 11]$ in $X$?
Any help would be very welcome! Thanks in advance.

$A^o=(0,2)\cup\{6\}\cup(10, 11]$. ($B_1(6)\cap X=\{6\}\subset A$...)
$ext A=(2,4]\cup \{10\}$
