Suppose Tommy decides to plant the gardenias. Which result would be a cost?
A: Tommy will give up the chance to look at the palm tree. He thinks it would have looked more beautiful than the gardenias.
B: He will save some space. The gardenias will use up less space than the palm tree would have used up.
This result is a cost. It involves giving up or spending something that Tommy wants or needs:
Tommy will give up the chance to look at the palm tree. He thinks it would have looked more beautiful than the gardenias.