Suppose Billy decides to plant the gardenias. Which result would be a cost?
Billy will give up the chance to look at the fir tree. He thinks it would have looked more beautiful than the gardenias. He will save some space. The gardenias will use up less space than the fir tree would have used up.
Billy is deciding whether to plant gardenias or a fir tree in his backyard. He wants to make his backyard more beautiful. But he also wants to leave space for doing fun things.
Before you decide to do something, it is often helpful to list costs and benefits.
Costs are what you give up or spend when you decide to do something. Costs involve giving up things that you want or need.
Benefits are what you gain or save when you decide to do something. Benefits involve gaining something that you want or need.
This result is a cost. It involves giving up or spending something that Billy wants or needs:
Billy will give up the chance to look at the fir tree. He thinks it would have looked more beautiful than the gardenias.