Over 5 of the floors, it takes the elevator 5 floors * 5 minutes per floor = <<5*5=25>>25 minutes to lower.
Over the final 5 floors, it takes the elevator 5 floors * 16 minutes per floor = <<5*16=80>>80 minutes to lower.
So in total, the elevator takes 15 minutes in the first half + 25 minutes in the next five floors + 80 minutes in the final five floors = <<15+25+80=120>>120 minutes to lower to the bottom.
This is the same as 120 minutes / 60 minutes per hour = <<120/60=2>>2 hours.
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