If $A$ and $B$ are any two sets, then $A \cup (A \cap B) $ is equal to

If $A=\{1,2,3,4\}, B=\{3,4,5,6\}, C=\{5,6,7,8\}$ and $D=\{7,8,9,10\} ;$ find

$A \cup B \cup D$

Let $A$ and $B$ be two sets such that $n(A) = 0.16,\,n(B) = 0.14,\,n(A \cup B) = 0.25$. Then $n(A \cap B)$ is equal to

If $X$ and $Y$ are two sets such that $X \cup Y$ has $50$ elements, $X$ has $28$ elements and $Y$ has $32$ elements, how many elements does $X$ $\cap$ $Y$ have?

Let $A=\{a, b\}, B=\{a, b, c\} .$ Is $A \subset B \,?$ What is $A \cup B \,?$