\[2c(5c - 3) - (c - 2)(c - 4) =\]
\[= 10c^{2} - 6c - \left( c^{2} - 4c - 2c + 8 \right) =\]
\[= 10c^{2} - 6c - c^{2} + 4c + 2c - 8 =\]
\[= 9c^{2} - 8.\]