text: 1.  D, due to basic properties and facts about energy.  In particular, you will use answer B to answer the other three questions.  Remember, energy is the product of power and time.\n\n2.  D, because E = Pt = (75 W)(90 s) = 6750 J\n\n3.  A, because t = E/P = (7000 J) / (100 W) = 70 s\n\n4.  A, because P = E/t = (6000 J) / (20 s) = 300 W