Okay this is what I have for Part A (company A only), but I cannot figure out where the 26% annual holding cost rate comes in to play. Any help figuring where I left this out and how to include is greatly appreciated!

EOQ = √2UP / C

Where: U = Annual usage in units =18,000

P = Ordering cost per order = 38

C = Carrying cost per unit =12

EOQ = √2UP / C => = √(2 x 18,000 x 38) / 12 => 337.6 or 338 units (after rounding)

Number of orders per year = U / EOQ => 18,000 units/338 = 53.25 or 53 orders (rounded)