Answer:
You included no options so I cannot help.
However, the number of boxes that Serena has must be in multiples of 7.
This is because each package is meant to hold 7 boxes so if she has several packages then in total she must have a number of boxes that is a multiple of 7.
For instance;
= 7, 14, 21, 28, 35, 42, 49, 56, 63, 70