If ${N_a} = \{an : n \in N\}$,then ${N_3} \cap {N_4} = $

The number of non-empty subsets of the set $\{1, 2, 3, 4\}$ is

Examine whether the following statement is true or false:
$\{a, b\} \not\subset \{b, c, a\}$

Which of the following sets is finite or infinite?
The set of prime numbers less than $99$.

If $A = \{1, 2, 3, 4, 5, 6\}$, then which of the following statements is not true?

Let $A = \{1, 2, 3, \ldots, 10\}$ and $B = \left\{\frac{m}{n} : m, n \in A, m < n \text{ and } \gcd(m, n) = 1\right\}$. Then $n(B)$ is equal to: