To find the unit rate, you need to divide the total number of books by the number of boxes.
So, you would calculate:
\[ \text{Books per box} = \frac{62 \text{ books}}{2 \text{ boxes}} \]
Calculating this gives:
\[ \text{Books per box} = 31 \text{ books per box} \]
Therefore, the unit rate is 31 books per box.