[tex]\it \overline{3,(x)} +\overline{3,0(x)}=6,4(8) \Rightarrow 3\dfrac{x}{9}+3\dfrac{x}{90}=6\dfrac{48-4}{90} \Rightarrow\\ \\ \\ \Rightarrow\dfrac{27+x}{9}+\dfrac{270+x}{90}=\dfrac{584}{90}|_{\cdot90} \Rightarrow270+10x+270+x=584 \Rightarrow\\ \\ \\ \Rightarrow 11x+540=584|_{_540}\Rightarrow 11x=44 \Rightarrow x=4[/tex]
