 Hi, Anthony. I got your email about the question on this problem of 6.1.29 and having to do with determining a sample size in for an estimate of the main given the values of C, the confidence level, sigma, and the margin of error. And it's really easy to do that using StatCrunch, which I don't know if you've been using that or not. But for some of these problems, I would suggest it is just very fast and very quick and very accurate. Your first question, though, was how do you get this C value, critical value of Z of 1.645? If we're given a confidence level of 0.9, alpha equals 1 minus 0.9 or 0.10, and you might be tempted to use 0.10 to go into the tables or into your calculator. But for a confidence interval, we're looking about the critical areas on either end of the normal distribution curve. And so we enter it with the tail area 0.05. Let's solve this using StatCrunch. And again, you can either call up StatCrunch from your question help tab there or go to statcrunch.com. Once you get StatCrunch open, we just go to StatCalculators, Normal, bring up this standard normal curve. I'm going to use the upper end just to be consistent. And all we need to enter in there is the alpha over 2.05. And if I am doing this right, we get a critical area there on the upper end. With a Z critical of 1.645. And that is the value they had there. And of course, your lower end, if I put in 0.05 again, alpha over 2, would be minus 1.645. So that is the critical value of C. Okay, I'm going to close that. And now let's use StatCrunch to calculate our end value. You can go through these long equations using Excel or a calculator if you want. But StatCrunch makes it very quick and easy. And when you're taking a quiz, I use all the tools I can get. We go to ZStats, one sample, power, sample width. And when we come up here, we want to click and click on the confidence interval width portion of the sample Z, power, sample size. All we have to enter in is the confidence level. Remember that's 0.90. Our standard deviation is, I think in your problem, 7.7. Now width, remember, is twice the margin of error. Our margin of error is 1. So I'm going to put 2 in there. And double check, I've got 0.9 for my confidence. 7.7 for my standard deviation. And a width of twice the margin of error 1, compute. And we get a sample size required of 161. And I think that is the answer that you got.