If $A$ and $B$ are disjoint, then $n(A \cup B)$ is equal to

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

$C-B$

If $A, B$ and $C$ are any three sets, then $A – (B \cap C)$ is equal to

If $\mathrm{R}$ is the set of real numbers and $\mathrm{Q}$ is the set of rational numbers, then what is $\mathrm{R – Q} ?$

If the sets $A$ and $B$ are defined as $A = \{ (x,\,y):y = {1 \over x},\,0 \ne x \in R\} $ $B = \{ (x,y):y =  – x,x \in R\} $, then