[tex]\displaystyle\bf\\\{12;x;y-6;6\}~i.p.~cu~\{4;3x;2;z\}\\\\12\cdot4=x\cdot3x=(y-6)\cdot2=6\cdot z\\\\48=3x^2=2(y-6)=6z\\\\a)\\3x^2=48~\Big|:3\\x^2=16\\x=\sqrt{16}\\x=\pm4\\\\b)\\2(y-6)=48~\Big|:2\\y-6=24\\y=24+6\\y=30\\\\c)\\6z=48~\Big|:6\\z=8[/tex]