A dog school trains labradors and golden retrievers to deliver newspaper. A labrador can deliver 7 newspapers at a time and requires 5 small bone treats for service. A golden retriever can deliver 10 newspapers at a time and requires 6 small bone treats per service. The school only has 1500 small bone treats available. In addition, at least 50 golden retrievers must be used and at most 60% of the dogs can be labradors. How many of each dog should be used to maximize the number of newspapers that can be delivered?