$(2$ marks$)$ Let $\backslash$Sigma $=\{$a$,$ b$\}$ and consider languages A $=\{$ab$,$ aa$,$ b$\},$ B $=\{$ba$,$ bb$,$ a$\}.$

$($a$)$ Write down all strings in the set A $$ B$.$ How many strings there are in A $$ B$?$

$($b$)$ Write down all strings in the set B $$ A$.$ How many string there are in B $$ A$?(2$ marks$)$ Let $\backslash$Sigma $=\{$a$,$ b$\}$ and consider languages A $=\{$ab$,$ aa$,$ b$\},$ B $=\{$ba$,$ bb$,$ a$\}.$

$($a$)$ Write down all strings in the set A $$ B$.$ How many strings there are in A $$ B$?$

$($b$)$ Write down all strings in the set B $$ A$.$ How many string there are in B $$ A$?$