And we kind of came up with this in the last video. So the mean of z, instead of writing z, I'm just going to write the mean of x. Let me do that same shade of green. The mean of x bar, which is the mean of x minus, or a sample from the sampling distribution of x, or the sample mean of x, minus the sample mean of y. So the mean of this is going to be equal to, and we saw this in the last video. In fact, I think I still have the work up here. Yeah, I still have the work right up here.