To find out how many books there are per box, we can divide the total number of books by the number of boxes.
Jori has 7 boxes and a total of 126 books:
\[ \text{Number of books per box} = \frac{\text{Total number of books}}{\text{Number of boxes}} = \frac{126}{7} \]
Calculating that gives us:
\[ \frac{126}{7} = 18 \]
So, there are 18 books per box.