Roberta does more total work than Mary. Mary does more total work than Roberta. Roberta has a greater power output than Mary. Mary has a greater power output than Roberta.
I gave my students this multiple choice question: Two students each carry a box up to the third floor of a building. The total mass of each student and the box she is carrying is the same. Roberta makes the trip in 45 s while Mary takes 30 s. Which of the following statements best describes this task?

Only one answer is correct among these 4 choices:
- Roberta does more total work than Mary.
- Mary does more total work than Roberta.
- Roberta has a greater power output than Mary.
- Mary has a greater power output than Roberta.

Could you tell me which one is correct?

Mary has a greater power output than Roberta.