And this is a property of expected values. I'm not going to prove it rigorously right here, but it's the expected value of X plus the expected value of Y. Or another way to think about this is that the mean of Z is going to be the mean of X plus the mean of Y. Or another way to view it is if I wanted to take, let's say I have some other random variable. I'm running out of letters here. Let's say I have the random variable A, and I define random variable A to be X minus Y. So what's its expected value going to be?