What universal set $(s)$ would you propose for each of the following :

The set of right triangles

Decide, among the following sets, which sets are subsets of one and another:

$A = \{ x:x \in R$ and $x$ satisfy ${x^2} - 8x + 12 = 0 \} ,$

$B=\{2,4,6\}, C=\{2,4,6,8 \ldots\}, D=\{6\}$

List all the elements of the following sers :

$E = \{ x:x$ is a month of a year not having $ 31 $ days ${\rm{ }}\} $

Which set is the subset of all given sets

Let $A, B$ and $C$ be three sets. If $A \in B$ and $B \subset C$, is it true that $A$ $\subset$ $C$ ?. If not, give an example.

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

$\{1,2,3\}\subset A$