A book dealer sells 600 books a year. He pays 20 euro per book. The order costs equal 25 euro and the annual holding costs are 0.75 euro per book.
Then the optimal order quantity is $q=\sqrt{\dfrac{2\cdot 25\cdot 600}{0.75}}=200$.
Then the optimal order quantity is $q=\sqrt{\dfrac{2\cdot 25\cdot 600}{0.75}}=200$.