We know that the sum of all of the data in a set = average * number of data.
Therefore, the sum of the first 10 is 1.5 * 10 = 15 meters, the sum of the second 10 is 1.48 * 10 = 14.8 meters and the sum of the last 2 is 1.6 * 2 = 3.2 meters for a total of 15 + 14.8 + 3.2 = 33 meters. This means that the mean is 33 / 22 = 1.5 meters.