Answer:
28 dollars, Christen sell 7 boxes and Rafael sell 4 boxes.
Step-by-step explanation:
We can make a list to see the rate of amount and dollars they got:
Boxes: 1, 2, 3, 4, 5, 6, 7, 8
Christen: 4, 8, 12, 16, 20, 24, 28, 32 ($)
Rafael: 7, 14, 21, 28, 35, 42, 49, 56 ($)
So the first one in common is 28 dollars, and just match them to the boxes, that's it.