\[\boxed{\mathbf{600\ (600).}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[= (51 - 38) \cdot \frac{5}{13} - \frac{2}{3} =\]
\[= \frac{13 \cdot 5}{13} - \frac{2}{3} = 5 - \frac{2}{3} = 4\frac{3}{3} - \frac{2}{3} =\]
\[= 4\frac{1}{3}\]
\[\boxed{\mathbf{600.}\mathbf{\ }}\]
\[6\% = 0,06\]
\[250 \cdot 0,06 = 15\ (кг) - соли.\]
\[Ответ:15\ кг.\]