Python 3.11.6 (main, Oct  3 2023, 00:00:00) [GCC 13.2.1 20230728 (Red Hat 13.2.1-1)] on linux
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  >>> population_base = [100_000_000, 1_000_000_000, 8_000_000_000]
  >>> for population in population_base:
  ...     print('15s/day for',population, 'people equals:', round((15*population)/3600), 'man-hours/day')
  ... 
  ...     
  15s/day for 100000000 people equals: 416667 man-hours/day
  15s/day for 1000000000 people equals: 4166667 man-hours/day
  15s/day for 8000000000 people equals: 33333333 man-hours/day