1 = 120 / tree = 120
2 = 60 / tree = 120
3 = 40 / tree = 120
4 = 30 / tree = 120
5 =24 / tree = 120
6 = 20 / tree = 120
7 = 17 / tree = 119
8 = 15 / tree = 120
9 = 13 / tree = 117
10 = 12 / tree = 120
11 = 11 / tree = 121
12 = 10 / tree = 120
13 = 9 / tree = 117
14 = 9 / tree = 126
15 = 8 / tree = 120
Take off one apple from #11 and give it to #7, and there is 120 apple in the 7th orchard
Take off three apple from #14 and give it to #13, and there is 120 apple in the 13rd orchard
Take off three apple from #14 and give it to #9, and there is 120 apple in the 9th orchard
15 X 120 =
1800 = ANSWER
it's the first time I got it all alone, so I decide to put it here because this board helped me a lot of time