The answer is 20 days, we can solve this in following way:
Each friend creates 4 bags of dough and after ten days four bags divided into four more bags means:
3 friends x 4 bags = 12 bags and 12 bags x 4 = 48 bags
so in next 10 days, the 48 bags will be further divided into 4, so
48 x 4 = 192 bags
10 days + next 0 days = 20 days
so 20 days is the answer.
