Hi! Try to be as pragmatic as possible.
1. Estimate average distance per usage --> assume the same probability for each level, hence 100 metres on average --> double the distance because the elevator needs to get back to the ground floor --> 200m per usage
2. Estimate number of usages per day --> here you need to consider number of elevators in the building and different times of the day (heavy usage in the morning and evening, medium usage mid day, very low usage at night)
3. Multiply 1 with 2 to get the total meters per day.