七.(本题满分8分)某人住家附近有一个公交车站,他每天上班时在该站等车的时间https://bgk-photo.cdn.bcebos.com/060828381f30e924f97863505c086e061c95f7f7.jpg(单位:分钟)服从https://bgk-photo.cdn.bcebos.com/80cb39dbb6fd5266d113c275bb18972bd4073692.jpg的指数分布,如果他候车时间超过https://bgk-photo.cdn.bcebos.com/9f510fb30f2442a7d43603c4c143ad4bd1130292.jpg分钟,他就改为步行上班.求他一周https://bgk-photo.cdn.bcebos.com/faedab64034f78f0ec33649269310a55b3191c92.jpg天上班时间中至少有https://bgk-photo.cdn.bcebos.com/1f178a82b9014a90df06b8dcb9773912b31bee93.jpg天需要步行的概率.