Answer:
The key to building suspense is making readers care about characters they slowly learn more about.
<span>As periods in mathematics we call groupings of large numbers (three-digits) usually separated by comma or space.
</span>
In this particular case we got two periods: 913 and 256.
Digits 913 are in the thousands period, while 256 in the units period.
It shows their plot as well as their friendship, and it shadows a future disagreement