Let $\displaystyle {S}$ be the universal set, where:
$\displaystyle {S}={\left\lbrace{1},{2},{3},\ldots,{28},{29},{30}\right\rbrace}$
Let sets $\displaystyle {A}$ and $\displaystyle {B}$ be subsets of $\displaystyle {S}$, where:

Set $\displaystyle {A}={\left\lbrace{1},{13},{16},{27},{28},{29}\right\rbrace}$

Set $\displaystyle {B}={\left\lbrace{1},{6},{18},{20},{21},{23},{25}\right\rbrace}$

Set $\displaystyle {C}={\left\lbrace{2},{7},{10},{12},{13},{15},{16},{17},{22},{23},{26},{28}\right\rbrace}$

Find the number of elements in the set $\displaystyle {\left({A}\cap{B}\right)}$
$\displaystyle {n}{\left({A}\cap{B}\right)}$ =

Find the number of elements in the set $\displaystyle {\left({B}\cap{C}\right)}$
$\displaystyle {n}{\left({B}\cap{C}\right)}$ =

Find the number of elements in the set $\displaystyle {\left({A}\cap{C}\right)}$
$\displaystyle {n}{\left({A}\cap{C}\right)}$ =

You may want to draw a Venn Diagram to help answer this question.