We may find the cumulative frequencies with their respective class intervals as below:
Cumulative frequency just greater than n2(i.e,302=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+(n2−cff)×h
=55+(15−136)×5
=55+106
=56.666
So, median weight is 56.67 kg.