(a) To find the mean, sum all the estimates and divide by the number of estimates:

\(\text{Mean} = \frac{4.1 + 4.2 + 4.4 + 4.5 + 4.6 + 4.8 + 5.0 + 5.2 + 5.3 + 5.4 + 5.5 + 5.8 + 6.0 + 6.2 + 6.3 + 6.4 + 6.6 + 6.8 + 6.9 + 19.4}{20} = \frac{123.4}{20} = 6.17\)

(b) To find the median, arrange the data in ascending order and find the middle value. Since there are 20 values, the median is the average of the 10th and 11th values:

\(\text{Median} = \frac{5.4 + 5.5}{2} = 5.45\)

(c) The median is more suitable because the mean is unduly influenced by the extreme value of 19.4, which skews the average higher than the central tendency of the majority of the data.