Explanation:

Summation of frequencies = 6+4+5+8+9+6+4 = 42

Median = mid value = average of 21^st and 22^nd value

Arranging data in increasing order we get
x        f
4        6
5        4
6        5
7        4
8        6
9        9
10      8

So mid value i.e 21^st and 22^nd value = 8