Exercise 13.5.2

[aituarov]

At the first part of solution, where you got planes with 100 at least, you need to filter like:
filter(!is.na(air_time)) , because filter(!is.na(tailnum)) count flights, that scheduled but didn't completed.

Page link: https://jrnold.github.io/r4ds-exercise-solutions/relational-data.html#filtering-joins