Rocky Mountain Tire Center sells $20,000$ go$-$cart tires per year.

The ordering cost for each order is $$40,$ and the holding cost is

$20\%$ of the purchase price of the tires per year. The purchase

price is as follows:

$$18$ per tire if $500$ order $<mn\; id="EditorElement\_882898">1</mn><mn\; id="EditorElement\_882899">0</mn><mn\; id="EditorElement\_882900">0</mn><mn\; id="EditorElement\_882901">0</mn>$

$$17$ per tire if $1000$ order

The supplier does not accept orders less than $500.$

How many tires should Rocky Mountain order each time it

places an order to minimize its total cost?