please explain in detail from where ( 400/ 400-250) came

please see attached

Given Annual demand D=60000 pairs Daily production p=400 Daily usage u=60000/240=250 Holding cost H=2.5 per month =2.512=$30 Set up cost S=$250 Q=H2DSpupQ=30260000250400250400Q=1633pairs b. Annual carrying cost =2Q(1pd)H=21633(1400250)30 Annual carrying cost =9185.625 c) Annual setup cost =(D/Q)S=(60000/1633)250=9185.548 d) Annual total cost = annual purchase cost + Annual carrying cost + annual setup cost =(15060000)+9185.625+9185.548=9000000+18371.25=9018371.25 e) Annual total cost = Annual carrying cost + annual setup cost =9185.625+ 9185.548=18371.25 f) production runs will be required per year =D/Q=60000/1633=36.74