Box A and Box B contained only black and red darts. In Box A, the ratio of the number of black darts to the number of red darts was 5 : 4. In Box B, the ratio of the number of black darts to the number of red darts was 5 : 1. There were 3 times as many darts in Box A as in Box B. What was the ratio of the number of black darts in Box A to the number of red darts in Box B? Give your answer in the simplest form.