fewer than $200$ tires are ordered, $$18$ per tire if $200$ or more$-$but fewer than $5,000-$ tires are ordered, and $$14$ per tire if $5,000$ or more tires are ordered

a$)$ How many tires should Rocky Mountain order each time it places an order?

Rocky Mountain's optimal order quantity is units $($enter your response as a whole number$).$

b$)$ What is the total cost of this policy?

Total annual cost of ordering optimal order size $=$$$,($round your response to the nearest whole number$)$