immutable" in line 18 is closest in meaning to,,,,unmatched|irregular|unnecessary|==unchangeable">

henceforth" in line 11 is closest in meaning to,,,,in the end|for a brief period|==from that time on|on occasion">

idea" mentioned in line 13 refers to,,,,the 60-hour workweek|the reduction in the cost of automobiles|==the reduction in the workweek at some automobile factories|the criticism of Ford by United States Steel and Westinghouse">