b.

6.

\(\Leftrightarrow\dfrac{11}{5}-x+\dfrac{3}{8}=-\dfrac{11}{40}\)

\(\Leftrightarrow\dfrac{11}{5}-x=\dfrac{11}{40}-\dfrac{3}{8}\\ \Leftrightarrow\dfrac{11}{5}-x=-\dfrac{1}{10}\\ \Leftrightarrow x=\dfrac{11}{5}+\dfrac{1}{10}\\ \Leftrightarrow x=\dfrac{23}{10}\)

7.

\(\Leftrightarrow\dfrac{3}{4}+x+\dfrac{4}{5}=-\dfrac{11}{20}\\ \Leftrightarrow\dfrac{3}{4}+x=-\dfrac{11}{20}-\dfrac{4}{5}\\ \Leftrightarrow\dfrac{3}{4}+x=-\dfrac{27}{20}\\ \Leftrightarrow x=\dfrac{-27}{20}-\dfrac{3}{4}\\ \Leftrightarrow x=\dfrac{-21}{10}\)

8.

\(\Leftrightarrow\dfrac{4}{9}-\dfrac{11}{8}+x=\dfrac{5}{72}\\ \Leftrightarrow\dfrac{-67}{72}+x=\dfrac{5}{72}\\ \Leftrightarrow x=\dfrac{5}{72}+\dfrac{67}{72}\\ \Leftrightarrow x=1\)

9.

\(\Leftrightarrow\dfrac{3}{4}+\dfrac{7}{5}+x=-\dfrac{6}{5}\\ \Leftrightarrow\dfrac{43}{20}+x=-\dfrac{6}{5}\\ \Leftrightarrow x=\dfrac{43}{20}+\dfrac{6}{5}\\ \Leftrightarrow x=\dfrac{67}{20}\)