4. You are part of a construction company that is supposed to build houses. An architect has left plans to build houses on each island. Bridges connect the islands. Island A and Island B have a total of 18 houses. Island A and Island C have a total of 16 houses. Island B and Island C have a total of 20 houses. A total of 27 houses is to be built on the three islands. Determine how many houses are to be built on each island.