If, Item= "A" , Demand of monthly= "n", Delivery time= "t" weeks and Lead time= "l" months. So how much the re-order qty?

ROL=Demand*Lead time + Safety stock, Demand=12n, Safety stock=n/30*t, ROL=12nt + nt/30, Re-order qty= ROL - Phy qty

Safety Stock, First In First Out Deliveries

Safety Stock: {Z * SQRT (Avg. Lead Time * Standard Deviation of Demand ^2 + Avg. Demand ^2 * Standard Deviation of Lead Time ^2)}. (note ^2 means ‘square’) Reorder Point: Average Lead Time*Average Demand + Safety Stock.

i will suggest to maintain a minimum of300 units each month,  If the lead time was 4 weeks I might carry 5 weeks