The median average refers to number in the middle of the set. But we need to write it in chronological order.
Now the set becomes 57, 60, 62, 65.
Now find the number in the middle. In this case, it both 60 and 62.
But we need one number.
So, we will take the average of both of them.
60 + 62 = 122
122 / 2 = 61
So, 61 is the median of the set.
EDIT:
Big thanks to mkersten for finding two errors in my answer!