i'm mining with bitminter client with my GPU that is an "ATI Radeon Caicos PRO Prototype" with a speed of 20Mhps.. how long does it take to make 1 bitcoin mining this way

does it worth it? or how to easily get bitcoins fast for free??? i don't wanna buy bitcoins...

You should not mine bitcoin with your GPU.
Check a profit calculator (for example:
https://bitcoinwisdom.com/bitcoin/calculator) and you will get the reason.
