\[\boxed{\text{310\ (310).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\(а)\ 1 - 1,7x - (0,8x + 2) = 3,4\)
\[1 - 1,7x - 0,8x - 2 = 3,4\]
\[- 2,5x = 3,4 + 1\]
\[- 2,5x = 4,4\]
\[x = 4,4\ :( - 2,5) = - 44\ :25\]
\[x = - 1,76\]
\[Ответ:x = - 1,76.\]
\[\textbf{б)}\ 5 - 0,2y = 0,3y - 39\]
\[- 0,2y - 0,3y = - 39 - 5\]
\[- 0,5y = - 44\ \]
\[y = - 44\ :( - 0,5) = 440\ :5\]
\[y = 88\]
\[Ответ:y = 88.\]