Most Helpful Girl
Since you're 17, I'm going to assume you are still in school and somewhat know the girls.
"Hey have you heard about ___ movie? " blah blah movie is good, trailer good "Do you wanna go see it this satuday at 4?" she agrees "it's a date"
Although if she starts inviting other people she's not interested or really oblivious.
Most Helpful Guy
Just straight up ask them out on a date. Don't be ambiguous or try to play it off as a joke. Be honest and bold.