There are 270 students at Colfax Middle School, where the ratio of boys to girls is 5:4. There are 180 students at Winthrop Middle School, where the ratio of boys to girls is 4:5. The two schools hold a dance and all students from both schools attend. What fraction of the students at the dance are girls?<spanclass=′latex−bold′>(A)</span>187<spanclass=′latex−bold′>(B)</span>157<spanclass=′latex−bold′>(C)</span>4522<spanclass=′latex−bold′>(D)</span>21<spanclass=′latex−bold′>(E)</span>4523