firstly you really shouldn't be helping anyone out with the expectation of getting sex, throw that idea out the window. But if you do want to help someone out who you find attractive think of it in steps.
The first step is that by helping her out, she's getting to know you. Don't just focus on what you're studying, try throwing in a fair amount of humour, show her your a fun guy to be around.
If you can do that, the rest will likely fall into place, and if it doesn't, brush it off and try again.
At the very least you should be able to become friends with a couple of these ladies and perhaps they have friends who would be into you. But you really have to lighten up, be humorous, have fun, and go with the flow.