For this question, perform the following:

remove rows with missing values

keep flights departing from airports $($ORIGIN$\_$AIRPORT$)$ that we want to look at $($BOS$,$ JFK$,$ SFO and LAX$)$

filter out the flights that have more than $1$ day delay $($DEPARTURE$\_$DELAY$)$

convert FLIGHT$\_$NUMBER column type to string

SCHEDULED$\_$DEPARTURE is coded as a float where the first two digits indicate the hour and the last two indicate the minutes. Convert this column to datetime format by combining existing columns DAY, MONTH, YEAR and SCHEDULED$\_$DEPARTURE

add IS$\_$DELAYED column by considering any flight with at least $15$ minutes delay $($DEPARTURE$\_$DELAY$)$ are delayed, and any other flight is not delayed

remove YEAR, MONTH, DAY columns

$[]$: def data$\_$preprocess$($flights$\_$df$)$:

# YOUR CODE HERE

raise NotImplementedError$()$

return $df$