1)电源电压为9V;
2)a.电压表3V:3=9×R2/(R2+20),3R2+60=9R2,R2=10;
b.电流表0.6A:0.6=9/(R2+20),0.6R2+12=9,R2=-5取0
电流表电流=9/20=0.45