A commercial cherry grower estimates from past records that if 18 trees are planted per acre, then each tree will yield an average of 32 pounds of cherries per season. If, for each additional tree planted per acre (up to 20 additional trees), the average yield per tree is reduced by 1 pound, how many trees should be planted per acre to obtain the maximum yield per acre? What is the maximum yield? In order to get the highest yield of pounds, trees should be planted per acre.