Well, it turns out, and I'm not proving it just yet, that the mean of the sum of random variables is equal to the sum of the means. So this is going to be equal to the mean of random variable X plus the mean of random variable Y. And so in this particular case, if I were to say, well what's the expected number of dogs and cats that I would see in a given day? Well, I would add these two means. It would be three plus four, it would be equal to seven. So in this particular case, it is equal to three plus four, which is equal to seven. And similarly, if I were to ask you the difference, if I were to say, well what's the, how many more cats in a given day would I expect to see than dogs, so the expected value of Y minus X?