You and a friend each carry a \(15 \mathrm{~kg}\) suitcase up two flights of stairs, walking at a constant speed. Take each suitcase to be the system. Suppose you carry your suitcase up the stairs in \(30 \mathrm{~s}\) while your friend takes \(60 \mathrm{~s}\). Which of the following is true? A. You did more work, but both of you expended the same power. B. You did more work and expended more power.

C. Both of you did equal work, but you expended more power.

D. Both of you did equal work, but you expended less power.