when was the first time that patient 71558 was prescribed with furosemide and aspirin ec at the same time?
select t1.startdate from ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'furosemide' and admissions.subject_id = 71558 ) as t1 join ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'aspirin ec' and admissions.subject_id = 71558 ) as t2 on t1.subject_id = t2.subject_id where datetime(t1.startdate) = datetime(t2.startdate) order by t1.startdate asc limit 1