hey what was patient 6215's average phenytoin, free value during the first hospital visit?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 6215 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'phenytoin, free' )