Two persons working 2 hours a day assemble 2 machines in 2 days. The number of machines assembled by 6 persons working 6 hours a day in 6 days is
Two persons working 2 hours a day in 2 days assemble 2 machines.
Two persons working 2 hours a day in 6 days assemble 6 machines
Two persons working 6 hours a day in 6 days assemble 18 machines
6 persons working 6 hours a day in 6 days assemble 54 machines