how many days have passed since patient 7112 received his first 5% dextrose prescription in the in this hospital visit?
select 1 * ( strftime('%j',current_time) - strftime('%j',prescriptions.startdate) ) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 7112 and admissions.dischtime is null ) and prescriptions.drug = '5% dextrose' order by prescriptions.startdate asc limit 1