a) \(\dfrac{x}{7}=\dfrac{-9}{21}\)
\(\Rightarrow\dfrac{x}{7}=\dfrac{-3}{7}\)
\(\Rightarrow x=-3\)
b) \(\dfrac{7}{x}=\dfrac{28}{-20}\)
\(\Rightarrow\dfrac{7}{x}=\dfrac{7}{-5}\)
\(\Rightarrow x=-5\)
c) \(\dfrac{-19}{3}=\dfrac{x}{-12}\)
\(\Rightarrow x=-\dfrac{19}{3}\cdot\left(-12\right)\)
\(\Rightarrow x=76\)
d) \(\dfrac{8}{-5}=\dfrac{40}{x}\)
\(\Rightarrow x=40:\dfrac{8}{-5}\)
\(\Rightarrow x=-25\)
e) \(\dfrac{2}{x}=\dfrac{8}{15}+\dfrac{-1}{20}\)
\(\Rightarrow\dfrac{2}{x}=\dfrac{29}{60}\)
\(\Rightarrow x=2:\dfrac{29}{60}\)
\(\Rightarrow x=\dfrac{120}{29}\)
f) \(\dfrac{x}{6}=\dfrac{-3}{5}+\dfrac{-7}{6}\)
\(\Rightarrow\dfrac{x}{6}=\dfrac{-53}{30}\)
\(\Rightarrow x=\dfrac{-53}{30}\cdot6\)
\(\Rightarrow x=\dfrac{-53}{5}\)
g) \(\dfrac{-9}{x}=\dfrac{-5}{12}+\dfrac{-7}{15}\)
\(\Rightarrow\dfrac{-9}{x}=\dfrac{-53}{60}\)
\(\Rightarrow x=-9:\dfrac{-53}{60}\)
\(\Rightarrow x=\dfrac{540}{53}\)
\(\text{#}Toru\)