Complex sentence: The girls who take part are in either Year 10,11 or 12 at high school (i.e. aged between 16 and 18), and the event is often used as a fund-raiser for local charities.
Split into simpler sentences: The girls who take part are in either Year 10,11 or 12 at high school (i.e. aged between 16 and 18). The event is often used as a fund-raiser for local charities.