54. a) \((\frac{1}{2}+\frac{3}{4})-(\frac{7}{8}-\frac{1}{2});\)

a) \((\frac{1}{2}+\frac{3}{4})-(\frac{7}{8}-\frac{1}{2}) = (\frac{1 \cdot 2}{2 \cdot 2} + \frac{3}{4})-(\frac{7}{8}-\frac{1 \cdot 4}{2 \cdot 4}) = (\frac{2}{4} + \frac{3}{4})-(\frac{7}{8}-\frac{4}{8}) = \frac{5}{4} - \frac{3}{8} = \frac{5 \cdot 2}{4 \cdot 2} - \frac{3}{8} = \frac{10}{8} - \frac{3}{8} = \frac{10-3}{8} = \frac{7}{8}\)

Ответ: \(\frac{7}{8}\)