4. Решите уравнение: a) 6 7/9 - x = 4 2/9; б) y + 2 6/7 = 5 3/7.

a) \(6 \frac{7}{9} - x = 4 \frac{2}{9}\)
\(x = 6 \frac{7}{9} - 4 \frac{2}{9}\)
\(x = (6 - 4) + (\frac{7}{9} - \frac{2}{9})\)
\(x = 2 + \frac{5}{9}\)
\(x = 2 \frac{5}{9}\)

б) \(y + 2 \frac{6}{7} = 5 \frac{3}{7}\)
\(y = 5 \frac{3}{7} - 2 \frac{6}{7}\)
\(y = 4 \frac{10}{7} - 2 \frac{6}{7}\)
\(y = (4 - 2) + (\frac{10}{7} - \frac{6}{7})\)
\(y = 2 + \frac{4}{7}\)
\(y = 2 \frac{4}{7}\)