. (5 points) A firm has three factories each producing the same item. Let x, y, z denote the respective output quantities that the three factories produce in order to fulfill an order of 2000 units in the total, namely rty+z2000. The cost of producing units of the item in the first factory is G (x) = 200 + 100x the cost of producing y units of the item and z units of the item in the second and third factories are, respectively: C2() 200++300 C3(2) 20010z Use the method of substitution to find the critical point (s) of the total cost function subject to the constraint that the total number of units produced must be equal to 2000