At the animal shelter where Miguel volunteers on the weekends, there were three Siamese cats, four tabby cats, fifteen mixed-breed dogs, and seven iguanas in their cages. If a customer picks any of these animals at random, find the probability that the animal is either a mixed-breed dog or a Siamese cat. Express your answer as a reduced fraction. The probability that the animal is either a mixed-breed dog or a Siamese cat is X