The cumulative frequency with their respective class intervals are as follows.

Cumulative frequency just greater than n/2 (i.e. 30/2 = 15) is 19, belonging to class interval 55 – 60.
Median class = 55 – 60
Lower limit (l) of median class = 55
Frequency (f) of median class = 6
Cumulative frequency (cf) of median class = 13
Class size (h) = 5
Median = l + ((n/2 – cf)/f) × h = 55 + ((15 – 13)/6) × 5 = 55 + 10/6 = 55 + 1.67 = 56.67.
Therefore, median weight is 56.67 kg.