(Inventory Cost) A shopkeeper finds that the cost C of ordering and storing the latest laptop is

C = 2 x + (300000 / x), where x is in the interval [1, 300]. The delivery of truck can bring at most 300 units per
order.
(a) Find the order size that will minimize the cost
(b) Could the cost be decreased if the truck is replaced with a larger one that could bring 400 units?

take the derivative of cost with respect to x. SEt it equal to zero. Solve for x.

I will be happy to critique your thinking.