Finding voltage gain and current gain using the load line in a common emmitor transistor amplifier
You seem to have almost solved the question. I will try to give you a hint how to continue. 

You know that distance QA (and QB) is 20uA. So you can see that +/- 20uA variation of Ib leads to ??? variation of Ic, which is the current gain. 

You can also draw A' and B' which are the corresponding points for (only) 12uA excitation (when we consider this as a linear problem).