12) \(37\frac{2}{21}-23\frac{5}{21}\)

Занимаем одну единицу: \(37\frac{2}{21}=36\frac{23}{21}\).

\(36\frac{23}{21}-23\frac{5}{21}=13\frac{18}{21}=13\frac{6}{7}\).

Ответ: \(13\frac{6}{7}\).