Write a regular expression for each of the following: $$ All strings over the alphabet $\{$a$,$b$\}$ with $\text{'}$ab$\text{'}$ as substring: $($a$|$b$)$ab$($a$|$b$)$

$$ all strings over the alphabet $\{$ a$,$ b $\}$ that contain exactly two a$\text{'}$s

$$ all strings over the alphabet $\{$ a$,$ b $\}$ that do not end with ab

$$ all strings over the alphabet $\{$ a$,$ b $\}$ that contain an even number of b$$s$.$

$$ all strings which do not contain the substring ba