The z-score of a certain data point in the given statistical data is calculated through the equation,
z-score = (x - m) / sd
where x is the data point, m is the mean and sd is the standard deviation.
Substituting the known values,
z-score = (51.8 - 52.3) / 1.8
z-score = -0.277
Rounding the answer to the nearest tenth will give an answer of -0.3.