20. Решите уравнение: а) (y − 8 12/19) + 1 7/19 = 6 2/19; б) (12 5/13 + y) − 9 9/13 = 7 7/13; в) (x − 3 13/21) + 2 10/21 = 7 2/21.

1. \((y-8\frac{12}{19})+1\frac{7}{19}=6\frac{2}{19}\).

   \(y=6\frac{2}{19}+8\frac{12}{19}-1\frac{7}{19}=13\frac{7}{19}\).

2. \((12\frac{5}{13}+y)-9\frac{9}{13}=7\frac{7}{13}\).

   \(y=7\frac{7}{13}+9\frac{9}{13}-12\frac{5}{13}=4\frac{11}{13}\).

3. \((x-3\frac{13}{21})+2\frac{10}{21}=7\frac{2}{21}\).

   \(x=7\frac{2}{21}+3\frac{13}{21}-2\frac{10}{21}=8\frac{5}{21}\).

Ответ: а) \(y=13\frac{7}{19}\); б) \(y=4\frac{11}{13}\); в) \(x=8\frac{5}{21}\).