In many cases, the shipping charges ( which are part of the reorder costs) vary with how many items are ordered. Suppose that the reorder costs are now R + Sx, where R is the cost of reording exclusive of shipping cost, and S is the shipping charge per item The cost function is now: C(x)= Hx/2 + D(R+Sx)/x Find the lot size, in terms of D, H, R and S, that will minimize the total costs.