Suppose Layla decides to plant the eucalyptus tree. Which result would be a cost?

 - The eucalyptus tree will use up more space than the hydrangeas would have used up.
 - Layla will get to look at the eucalyptus tree. She thinks it will look more beautiful than the hydrangeas would have looked.
This result is a cost. It involves giving up or spending something that Layla wants or needs:
The eucalyptus tree will use up more space than the hydrangeas would have used up.