6. On six oaks, there were 129 birds. At one moment, 6 flew away from the first, 11 from the second, 8 from the third, 10 from the fourth, 7 from the fifth, and 9 from the sixth oak. Then, an equal number of birds remained on each oak. How many birds were there on each oak at the beginning?
6. $129-(6+7+8+9+10+11)=129-51=78$
After 51 birds flew away, 78 birds remained on 6 oaks. ..... 2 points
$78: 6=13$
On each of them, 13 birds remained. ..... 2 points
At the beginning, there were $13+6=19$,
on the second $13+11=24$
on the third $13+8=21$,
on the fourth $13+10=23$,
on the fifth $13+7=20$
and on the sixth $13+9=22$ birds. 6 points
TOTAL 10 POINTS