Find the cardinal number of the following set $\{x: x\}$ is a natural number $\leq 30$ and is divisible by $7$ or $\{11\}$

Two finite sets have $m$ and $n$ elements. The total number of subsets of the first set is $56$ more than the total number of subsets of the second set. The values of $m$ and $n$ are

If $f(x) = a\cos(bx + c) + d$,then the range of $f(x)$ is

If $U = \{a, b, c, d, e, f\}$,$A = \{a, b, c\}$,$B = \{c, d, e, f\}$,and $C = \{c, d, e\}$,find $(A \cup B) \cup C$.

If $aN = \{ ax : x \in N \}$,then the set $3N \cap 7N$ is equal to .....$N$.

If $A$ and $B$ are two sets,then $A \times B = B \times A$ if and only if