54. a) \(\frac{7}{8}=\frac{x}{6}\)
Решим пропорцию:
\(8 \cdot x = 7 \cdot 6\)
\(8x = 42\)
\(x = \frac{42}{8} = \frac{21}{4} = 5\frac{1}{4} = 5,25\)
Ответ: \(x = 5,25\)