10 peoples can build a wall in 12 days. six peoples, each only half as efficient as those in the first group, will be able to complete 3/5 of such a wall in?

Let the total work done be 120 units.
Work done by 10 people per day = 120/12 = 10 units /day
Work done per person = 10/10 = 1 unit/day
In the next team, each person is half as efficient as the previous one.
Hence work done per person = 0.5/day
3/5 * 120 = 72 , work which needs to be done by team 2
Hence time taken will be,
6 * 0.5 * x = 72
=> x = 24

24