Implement the extract$\_$years function, which accepts a string file$\_$name. The function builds and returns a list of birth years $($integers$!)$ of the teachers. Their names are ignored.

$2.$ Implement the function full$\_$name$\_$of$\_$oldest, which accepts a string file$\_$name. The function determines and returns the full name $($first and last name, separated by a space$)$ of the oldest teacher.