\[(3,1x + x)\ :0,8 = 2,05\]
\[x(3,1 + 1) = 2,05 \cdot 0,8\]
\[4,1x = 1,64\]
\[x = 1,64\ :4,1\]
\[x = 0,4\]
\[Ответ:\ x = 0,4.\]