For now, imagine you just have clown and angel fish. 5/9 of the fish are clown, and 4/9 angel. This means that 60 = 5/9, so 1/9 is 12, and so 4/9 is 48. There are 48 angel fish. Now ignore the clowns, we have 48 angel fish, which is 4/7, and the other 3/7 is goldfish. if 4/7 = 48, then 1/7 is 12, and so 3/7 is 36. There are 60 clown fish, 48 angel fish and 36 goldfish.