Spaceship I, which contains students taking a physics exam, approaches Earth with a speed of 0.60c, while spaceship II, which contains instructors proctoring the exam, moves at 0.28c (relative to Earth) directly toward the students. If the instructors in spaceship II stop the exam after 50 min have passed on their clock, how long does the exam last as measured by (a) the students (b) An observer on the Earth?