Question: what are all the possible combinations of 4 numbers?
Answer: With respect to that technical meaning, there is only one combination of the four numbers 4, 5, 8, and 7, taken four at a time: All four of them. There are 24 combinations. 4578, 4587, 4758, 4785, 4857, 4875, 5478, 5487, 5748, 5784, 5847, 5874, 7458, 7485, 7548, 7584, 7845, 7854, 8457, 8475, 8547, 8574, 8745, and 8754.