In order to get in shape for mountain climbing, an avid hiker with a mass of 60. kg ascends the stairs in the world’s tallest structure, the 828 m tall Burj Khalifa in Dubai, United Arab Emirates. Assume that she eats energy bars on the way up and that her body is 25% efficient in converting the energy content of the bars into the work of climbing. How many energy bars does she have to eat if a single bar produces 1.08 × 10³ kJ of energy upon metabolizing?