\[x\frac{км}{ч - скорость\ течения;}\]
\[\frac{16}{x}\ ч - по\ течению;\]
\[\frac{1}{6 - x}\ ч - против\ течения.\]
\[16 \cdot (6 - x) + 16x = 12x(6 - x)\]
\[12x^{2} - 72x + 96 = 0\ \ \ \ \ \ |\ :12\]
\[x^{2} - 6x + 8 = 0\]
\[D = ( - 6)^{2} - 4 \cdot 1 \cdot 8 =\]
\[= 36 - 32 = 4;\ \ \ \ \sqrt{D} = 2.\]
\[x_{1} = \frac{6 + 2}{2} = \frac{8}{2} = 4;\ \ \ \]
\[\text{\ \ }x_{2} = \frac{6 - 2}{2} = \frac{4}{2} = 2\]
\[Ответ:4\frac{км}{ч\ \ или\ 2\ \frac{км}{ч.}}\]