I only need 10$. How much does it take to earn than with a i7 2.2 ghz system?
Forever.
Just forget it. Mining bitcoin without specialized mining hardware is not going to work anymore (hint: by the time you or your children eventually reach 10$, you've spent a fortune on energy and computer replacements to keep your "miner" running).
To calculate approximate mining results:
- look up your CPU here:
https://en.bitcoin.it/wiki/Non-specialized_hardware_comparison#Intel- take the ghash/s value and enter it at the mining calculator
https://bitcoinwisdom.com/bitcoin/calculatorEnter 0 for hardware price, pool fee and electricity costs (otherwise you'll only get negative revenue). Since I don't know your exact CPU model, I've entered 10 ghash/s which is probably generous.
You'll see that you will have gotten around 1.62$ by September 2016. Difficulty will increase further, so that's about all you will ever get (the calculator does not compute beyond that time, but that would not make sense anyway). With a difficulty increase of about 2% you'd get 10$ eventually, but that's very unreasonable to assume.
Comclusion:
If you need 10$, work some hours (depending on the wage you can get in your country and given your skills) and get paid for your work.
If you need bitcoins worth 10$, get 10$ as described above, and buy bitcoins.
Onkel Paul