If $A$ is any set,then:

Let $U=\{1, 2, 3, 4, 5, 6, 7, 8, 9\}$,$A=\{1, 2, 3, 4\}$,$B=\{2, 4, 6, 8\}$,and $C=\{3, 4, 5, 6\}$. Find $(A \cup B)'$.

Two dice are thrown. The events $A, B$ and $C$ are as follows:
$A:$ getting an even number on the first die.
$B:$ getting an odd number on the first die.
$C:$ getting the sum of the numbers on the dice $\leq 5$.
Describe the event $\text{not } B$.

Let $U$ be the set of all triangles in a plane. If $A$ is the set of all triangles with at least one angle different from $60^{\circ},$ what is $A^{\prime}$?

Let $U = \{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 \}$,$A = \{ 1, 2, 5 \}$,and $B = \{ 6, 7 \}$. Then $A \cap B'$ is:

Taking the set of natural numbers as the universal set,write down the complement of the following set:
$A = \{ x : x \text{ is an odd natural number} \}$