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)
To find the number of days it will take Milly to sell 56 boxes, we need to divide the total number of boxes by the number of boxes she sells in a given time period.
First, we divide 56 boxes by 8 boxes to find out how many groups of 8 boxes she sells: 56 boxes / 8 boxes/group = 7 groups
Since Milly sells 8 boxes every 3 days, we multiply the number of groups by the number of days it takes to sell 8 boxes: 7 groups * 3 days/group = <<7*3=21>>21 days.
Therefore, it will take Milly 21 days to sell 56 boxes of cookies. Answer: \boxed{21}.