count the number of times patient 15754 was tested for mch in 2104.
select count(*) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'mch' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 15754 ) and strftime('%y',labevents.charttime) = '2104'