Bell Entertainment sells souvenir T$-$shirts at each rock concert that it sponsors. The shirts cost $$7$ each. Any excess shirts returned to the manufacturer for a full refund of the purchase price. The sales price is $$16$ per shirt.

Required

a$.$ What are the total cost of shirts and cost per shirt if sales amount to $2,000,2,500,3,000,3,500,$ or $4,000?$

b$.$ Is the cost of T$-$shirts a fixed or a variable cost?