This is the 3368th most frequent Russian word.
полезными
"Полезными" means "useful" or "beneficial" in English.
The word 'полезными' (useful/beneficial) is used as an instrumental plural adjective describing 'фрукты' (fruits) in terms of health benefits.
Фрукты полезными для здоровья.
Fruits are beneficial for health.
The word 'полезными' is the instrumental plural form of 'useful,' indicating the role or function of the 'совет' (advice).
Этот совет оказался весьма полезными.
This advice turned out to be very useful.
Here, 'полезными' describes the resultant state of tasks in the instrumental mood after applying the tool.