If one class needs the most, the other six classes must be as few as possible, because the number of each class is different, so the other six classes can only have at least 1, 2, 3, 4, 5 and 6 trees, totaling 2 1, so the seventh class will have the most,100-2/kloc.

That's completely different, but the idea is the same, so from 18 down, take six maximum values18+17+16+15+14+.

Only by planting as many trees as possible can the seventh category be worthless, and the seventh category must plant at least 100-93=7 trees.