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

$Y-X$

If $A=\{3,6,9,12,15,18,21\}, B=\{4,8,12,16,20\},$ $C=\{2,4,6,8,10,12,14,16\}, D=\{5,10,15,20\} ;$ find

$A-D$

If $A$ and $B$ are two sets such that $A \subset B$, then what is $A \cup B ?$

If $aN = \{ ax:x \in N\} ,$ then the set $3N \cap 7N$ is .....$N$

If $A=\{x \in R:|x|<2\}$ and $B=\{x \in R:|x-2| \geq 3\}$ then

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

$A \cap B$