Milly is selling Girl Scout cookies. She sells 8 boxes every 3 days. How many days will it take her to sell 56 boxes? (1 point)
7 days
10 days
12 days
21 days
Milly sells 8 boxes every 3 days, so she sells 8/3 = <<8/3=2.6667>>2.6667 boxes every day.
To sell 56 boxes, it will take her 56/2.6667 = <<56/2.6667=21>>21 days.
Therefore, it will take her 21 days to sell 56 boxes. Answer: \boxed{21}.