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?

  Options: 
 A. Roberta does more total work than Mary.
 B. Mary does more total work than Roberta.
 C. Roberta has a greater power output than Mary.
 D. Mary has a greater power output than Roberta. 
Answer: D