Đáp án:

`x = -\frac{1}{3}`

Giải thích các bước giải:

`b,` `\frac{11}{15} - (\frac{7}{9} + x) \times \frac{3}{8} = \frac{61}{90} + \frac{x}{3}`

`<=> \frac{11}{15} - [(\frac{7}{9} + x) \times \frac{3}{8} + \frac{x}{3}] = \frac{61}{90}`

`<=> (\frac{7}{9} + x) \times \frac{3}{8} + \frac{x}{3} = \frac{11}{15} - \frac{61}{90}`

`<=> \frac{7}{24} + \frac{3}{8}x + \frac{1}{3}x = \frac{5}{90}`

`<=> \frac{7}{24} + \frac{17}{24}x = \frac{1}{18}`

`<=> \frac{17}{24}x = \frac{1}{18} - \frac{7}{24}`

`<=> \frac{17}{24}x = -\frac{17}{72}`

`<=> x = -\frac{17}{72} \times \frac{24}{17}`

`<=> x = -\frac{1}{3}`

Vậy `x = -\frac{1}{3}`