Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$

Write the subset relations between the following sets.

X = set of all quadrilaterals.

Y = set of all rhombuses.

S = set of all squares.

T = set of all parallelograms.

V = set of all rectangles.

If M is any set, then write $M\cup \phi$ and $M\cap \phi$.

Observe the Venn diagram and write the given sets $U, A, B, A\cup B$ and $A\cap B$.

If $n\left(A\right)=7, n\left(B\right)=13, n\left(A\cap B\right)=4$, then $n\left(A\cup B\right)=?$