Simple Saris is a retailer of women's fashion. They purchase garments in lots from a supplier and then sell them to customers in their store. It costs $$5$ to store one garment for a year. To reorder more garments from their supplier, Simple Saris pays a fixed fee of $$20$ per lot as well as a per garment fee of $$4.$ They sell $750$ garments each year.

Find a function that models their total inventory costs $($in dollars$)$ as a function of

the lot size for each of their orders from the supplier.