The z-score for 55.2 is 0.25.
Explanation: Using the Standard Normal Table, the area to the left of 0.25 is 0.5987, and the area to the left of 0.5 is 0.6915. As 0.6915−0.5987=0.0928, the probability that the sample mean is in between 55.2 inches and 55.4 inches is approximately 9%.