Is it possible to average up to certain row indicated in "Last number to average" or C8

A B C
1 5
2 7
3 8
4 10
5 6
6 10
7
8 Last number (NO.) to average: 4 (i would like to average from A1 to A4)

REsult = 7.5 or (5+7+8+10)/4

Thanks much