The local cable company has a main station located on a stretch of straight coastline. A small island lies twenty miles down the coast from the main office and five miles offshore. In order to supply service to the island, the cable company needs to run underground cable from the main station to a substation on the island. The cost for laying the cable is $30,000 per mile along the coast, but the cost for laying the cable under the ocean is $42,000 per mile. What is the minimum cost for connecting the two stations, and how can this be achieved?