My father worked as a police officer for forty years until last year.
Koichi served an important role of taking care of aliens from various planets.
Mr. Tamura was employed as Ms. Tanaka’s private secretary for one year, but it didn’t really work out.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means task so what's the verb vocab version? Well, when you do a task, you are going to work as or to serve as something to do that task.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
To work as my secretary, you will have to complete a task. A task where you bring me two toes (つと)! Don't ask me why! You want to serve as my assistant, right? Just get me those two toes then!