Celeste wants to have her hair cut and permed and also go to lunch. she knows she will need $50. the perm costs twice as much as her haircut and she needs $5 for lunch.

I assume you would like to know the cost of her perm and haircut, so thats what I will answer. 

She needs $5 for lunch, and er perm will cost twice as much as her haircut. We have $45 left, so we can divide it by three (because the perm will cost twice as much as the haircut, as this why we can figure out how much that is) 45÷3 is 15.

So now we know her haircut will cost $15 and her perm will cost $30.