if doable, find a regular expression for the following languages over alphabet $\{$a$,$ b$\}.$

i$.$ Strings with an odd number of a

ii$.$ Both the number of a$\text{'}$s and the number of b$\text{'}$s are even

iii. No string contains the substring aa

iv$.\{$a$2$n $|$ n $$ N$\}$ U $\{$b$2$n$+1|$ n $$ N$\}$ while N$=\{0,1,2,3,...\}$