\[4,35 \cdot (3,04 - c) = 6,09\]
\[3,04 - c = 6,09\ :4,35\]
\[3,04 - c = 1,4\]
\[c = 3,04 - 1,4\]
\[c = 1,64\]
\[Ответ:\ c = 1,64.\]