Graphing the set of data in a dot plot, we have:
Since this set has 18 elements, the median is the average between the 9th and 10th elements using the set in the crescent order.
Looking at the dot plot, the 9th element is 7 and the 10th element is 8, so the median is (7 + 8)/2, that is, the median is 7.5.