Assume that an agribusiness firm uses a particular liquid chemical in their production of herbicide. The firm uses 4900 litres of this chemical per year and spends K50 every time they place an order. Assume further that the supplier of this chemical offers the firm a price of K5 per litre for purchases below 999 litres. Nevertheless, purchases between 1000 and 3999 litres cost K4.95 per litre while 4000 to 5999 litre purchases costs K4.90 per litre. The supplier further quotes a price of K4.85 for any purchases of 6000 litres and above. 

a) If annual carrying costs are 40 percent of unit cost, what is the optimal order size? 

b) If carrying costs are K2 per year for each liter, find the order quantity that will minimize total annual cost. 

c) If lead time is six working days and the company operates 250 days in a year, at what point should the company reorder?