The greatest common factor of 9, 12, and 18 is 3, so we know that we can make at most 3 identical lunchboxes. Now we have to divide each number by 3 to figure out how much of each item is in each lunchbox. 9/3=3, 12/3=4, and 18/3=6 so there will be 3 carrots, 4 crackers, and 6 grapes in each lunchbox.
