Answer
$S=\{ so,sr,se,os,or,oe,rs,ro,re,es,eo,er\}$
$E=\{os,or,oe,es,eo,er\}$
Work Step by Step
Sequences beginning with "s": so,sr,se.
Sequences beginning with "o": os,or,oe
Sequences beginning with "r": rs,ro,re.
Sequences beginning with "e": es,eo,er.
Sequences beginnning with a vowel : os,or,oe,es,eo,er
$S=\{ so,sr,se,os,or,oe,rs,ro,re,es,eo,er\}$
$E=\{os,or,oe,es,eo,er\}$
