when did patient 20441 get admitted to the hospital via the hospital er admit for the last time since 4 years ago?
select admissions.admittime from admissions where admissions.subject_id = 20441 and admissions.admission_location = 'emergency room admit' and datetime(admissions.admittime) >= datetime(current_time,'-4 year') order by admissions.admittime desc limit 1