Answer:
12 people
Explanation:
On the morning of the 3rd day, there are 4 working days (of the 6 days) left for 12-person crew, or 4*12 = 48 man.days
The team completed the remaining job in 2 days. This means 48 / 2 = 24 people helped complete the task.
So the number of new workers who joined the crew is
24 - 12 = 12 people