Make correct statements by filling in the symbols $\subset$ or $ \not\subset $ in the blank spaces:

$\{ x:x$ is a triangle in a plane $\}  \ldots \{ x:x$ is a rectangle in the plane $\} $

Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?

$\{ 3,4\}  \subset A$

Write the following intervals in set-builder form :

$\left[ {6,12} \right]$

Write the following as intervals :

$\{ x:x \in R,3\, \le \,x\, \le \,4\} $

List all the subsets of the set $\{-1,0,1\}.$

Write the following intervals in set-builder form :

$\left[ { - 23,5} \right)$