\[ \frac{3}{7}x + 5\frac{1}{2}x - 7\frac{3}{4} = 1 - \frac{4}{7}x + 5\frac{1}{4}x \]
\[ \frac{3}{7}x + \frac{11}{2}x - \frac{31}{4} = 1 - \frac{4}{7}x + \frac{21}{4}x \]
\[ \left( \frac{3}{7} + \frac{11}{2} + \frac{4}{7} - \frac{21}{4} \right)x = 1 + 7\frac{3}{4} \]
\[ \left( \frac{12}{28} + \frac{154}{28} + \frac{16}{28} - \frac{147}{28} \right)x = 1 + \frac{31}{4} \]
\[ \left( \frac{12 + 154 + 16 - 147}{28} \right)x = \frac{4}{4} + \frac{31}{4} \]
\[ \frac{35}{28}x = \frac{35}{4} \]
\[ \frac{5}{4}x = \frac{35}{4} \]
\[ x = \frac{35}{4} \div \frac{5}{4} \]
\[ x = \frac{35}{4} \times \frac{4}{5} \]
\[ x = \frac{35}{5} \]
\[ x = 7 \]
Ответ: 7