An apple farm yields an average of 44 bushels of apples per tree when 24 trees are planted on an acre of ground. Each time 1 more tree is planted per acre, the yield decreases by 1 bushel (bu) per tree as a result of crowding. How many trees should be planted on an acre in order to get the highest yield?
In order to get the highest yield ______ trees should be planted on an acre.