I have the possibility to get a used computer for zwift, here are the spec


what do you think

My i3 with intel hd just dont work


 AMD FX-6100 six-core 3.3GHz
Motherboard: Gigabyte 970A-UD3P AMD970
: Nvidia GeForce 660 ti directx
: 8Gb 2 x 4Gb DDR3-1866

Check this minimum requirements page:

Since Zwift relays on graphics you should check your graphics card. I think you are (more than) good to go:

The Intel HD 4000 is being used as reference card is this comparison.

You’ll be fine.
I have an AMD Phenom II 4 cores from 2009 and a 2010 1GB HD5770 graphic card. The graphics are not super sharp but it works just fine, your card and processor are more powerful.