Suppose the cost, in dollars, of producing $x$ items is $C(x)=100 x+2000 / x$ Determine (a) the cost of producing 50 items, (b) the cost of producing the 50th item, the marginal cost when $x=50,$ (c) the average cost function, (d) the average cost of producing 50 items, (e) estimate the level of production which minimizes the cost and estimate the minimum cost.