If $n(A) = 3$, $n(B) = 6$ and $A \subseteq B$. Then the number of elements in $A \cup B$ is equal to

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 $X=\{a, b, c, d\}$ and $Y=\{f, b, d, g\},$ find

$X-Y$

If $A, B$ and $C$ are non-empty sets, then $(A -B)  \cup (B -A)$ equals 

If $X=\{a, b, c, d\}$ and $Y=\{f, b, d, g\},$ find

$Y-X$

If $A = \{ x:x$ is a natural number $\} ,B = \{ x:x$ is an even natural number $\} $ $C = \{ x:x$ is an odd natural number $\} $ and $D = \{ x:x$ is a prime number $\} ,$ find $A \cap D$