4. Решите уравнение: а) \((x - 1 \frac{8}{9}) + 3 \frac{7}{9} = 4 \frac{4}{9};\) б) \((3 \frac{9}{13} + x) - 4 \frac{9}{13} = 1 \frac{7}{13}.\)

\(x - 1 \frac{8}{9} = 4 \frac{4}{9} - 3 \frac{7}{9}\)

\(x - 1 \frac{8}{9} = 3 \frac{13}{9} - 3 \frac{7}{9}\)

\(x - 1 \frac{8}{9} = \frac{6}{9}\)

\(x = \frac{6}{9} + 1 \frac{8}{9}\)

\(x = 1 \frac{14}{9}\)

\(x = 2 \frac{5}{9}\)

\(3 \frac{9}{13} + x = 1 \frac{7}{13} + 4 \frac{9}{13}\)

\(3 \frac{9}{13} + x = 5 \frac{16}{13}\)

\(x = 5 \frac{16}{13} - 3 \frac{9}{13}\)

\(x = 2 \frac{7}{13}\)