a) \( x + \frac{4}{5} = 1 \frac{9}{10} \)

Решение:

\( x = 1 \frac{9}{10} - \frac{4}{5} \)

\( x = \frac{19}{10} - \frac{8}{10} \)

\( x = \frac{11}{10} \)

\( x = 1 \frac{1}{10} \)

Ответ: \( x = 1 \frac{1}{10} \)