4. A sporting goods store sells 520 surfboards per year. It costs $3 to store one surfboard for one year. To reorder, there is a fixed cost of $5, plus $3.50 for each surfboard. a) Find the total inventory cost function in term of x. b) To minimize the inventory cost, how large is the lot size? c) How many times per year should the store order surfboards and ? And what is the total inventory cost? 4. A sporting goods store sells 520 surfboards per year. It costs $3 to store one surfboard for one year. To reorder, there is a fixed cost of $5, plus $3.50 for each surfboard. a) Find the total inventory cost function in term of x. b) To minimize the inventory cost, how large is the lot size? c) How many times per year should the store order surfboards and ? And what is the total inventory cost