I get a z-value of 2.62, off of which I got a P-value for a 2-tailed test .008703. It says my P-val is correct, my z-value is incorrect. Do I just double this z-value bc it's a 2-tailed test?

Total blood volume (in ml) per body weight (in kg) is important in medical research. For healthy adults, the red blood cell volume mean is about = 28 ml/kg. Red blood cell volume that is too low or too high can indicate a medical problem. Suppose that Roger has had seven blood tests, and the red blood cell volumes were as follows.

30

23

41

37

32

37

29

Let x be a random variable that represents Roger's red blood cell volume. Assume that x has a normal distribution and = 4.75. Do the data indicate that Roger's red blood cell volume is different (either way) from = 28 ml/kg? Use a 0.01 level of significance.