A factory has two classifications for its workers, A and B. Class A receive $14 per journey and those in Class B receive $13 per journey. For a certain production lot, there is determined that if X workers of class A and Y workers of class B work, the cost of the lot will be: y3 + x2 - 8xy + 600 How many workers of each class must be employed, in such a way that the cost of the lot is minimal, if at least three workers of each class are required for its manufacture