Demand for an item is $20309$ units per year. Each order placed costs $$101.$ The annual carrying cost percentage per item in inventory is $20\%$ each. The variable purchase cost is $$2\mathrm{.}50$ per unit if less than $3000$ units will be ordered, $$2\mathrm{.}40$ from $3000$ units upto $($but not including $4000$ units$),$ and $$2\mathrm{.}30$ for at least $4000$ units. These are all$-$units discounts.