State whether the following set is finite or infinite:
The set of numbers which are multiples of $5$.

Write the following set in the set-builder form: $\{ 5, 25, 125, 625 \}$

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

If ${N_a} = \{an : n \in N\}$,then ${N_5} \cap {N_7} = $

If $A = \{x \in \mathbb{R} : x^2 + 5|x| + 6 = 0\}$,then $n(A) = $

Given the sets $A = \{1, 3, 5\}$,$B = \{2, 4, 6\}$,and $C = \{0, 2, 4, 6, 8\}$,which of the following sets can be considered as a universal set for all the three sets $A$,$B$,and $C$?
$X = \{0, 1, 2, 3, 4, 5, 6\}$