We know that, median is the middle most observation.
For finding the median of the data firstly, we arrange the data in ascending order.
i.e. Ascending order is 3, 3, 4, 4, 5, 6, 7.
n = 7 (odd)
∴ Median = Value of (n+12)th observation = Value of (7+12)th observation
= 4th observation = 4