That 9.2 can be viewed as a sample from this distribution right over here. Same thing if this right here is m. Or if m right here is 12. You're taking 12 samples, taking its mean. And that sample mean, maybe it's 15.2, could be viewed as a sample from this distribution, as a sample from the sampling distribution. So what z is, z is a random variable where you're taking n samples from this distribution up here, this population distribution, taking its mean. Then you're taking m samples from this population distribution up here, taking its mean, and then finding the difference between that mean and that mean. So it's another random variable.