\(a.\dfrac{1}{4}+\dfrac{3}{4}x=-0,3\)
\(\Leftrightarrow\dfrac{3}{4}x=-\dfrac{11}{20}\)
\(\Leftrightarrow x=-\dfrac{11}{15}\)
\(b.\dfrac{4}{7}x-\dfrac{7}{3}=\dfrac{1}{21}\)
\(\Leftrightarrow\dfrac{4}{7}x=\dfrac{50}{21}\)
\(\Leftrightarrow x=\dfrac{25}{6}\)