To find the answer to this question just divide 139 by 8.
8 goes into 13 once.
8 goes into 59 7 times.
So the answer is 17 remainder 3.
Since all the pencils won't fit into 17 boxes, she'll have to get another box for the last three pencils.
So the answer is 18.
Hope this helped! If you have anymore questions or don't understand, please comment on my profile or DM me. :)