You can also try it with gambling but I do not recommend that.
But what if you can't afford buying another 10 bitcoin? There is a saying that no pain no gain. The only way to make it 17 btc from 7 btc is by investing it and taking risks. If you are afraid to lose your 7 bitcoin then try only soms few amounts at first. Amd when you are confident on what you are doing, make your capital bigger and you will earn 17 btc without knowing it.
that is not the only way!
the best way that normal people use is to get a job and work. so you can get a salary that way that you can then buy bitcoin with that salary or part of it.
i agree get a full time job in your place then you can earn a lot it is a stable job than bitcoin. make the bitcoin as a sideline dude.