Okay, let's solve this step-by-step:
* The original scenario: 5 people working 6 hours per day.
* Each person works 6*5 = 30 hours per day total for the 5 people
* The task takes 16 days with this setup
* The new scenario: 8 people working 4 hours per day
* Each person now works 4 hours, so total hours per day for 8 people is 4*8 = 32 hours
* We want to know how many days this will take them.
* Since they now work 32 hours per day instead of the original 30 hours, that means they do 32/30 = 1.07 times more work each day
* So the number of days it will now take them is the original 16 days divided by 1.07, which is approximately 15 days
So the answer is: 15 days