[tex]a)\ \dfrac{x+7}{5} =\dfrac{ \ 84^{(7}}{35} \Rightarrow \dfrac{x+7}{5} =\dfrac{12}{5} \Rightarrow x+7 =12 \Rightarrow x = 5
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b)\ \dfrac{3}{2x-1} = \dfrac{\ \ 7^{(7}}{21} \Rightarrow \dfrac{3}{2x-1} =\dfrac{1}{3} \Rightarrow \dfrac{2x-1}{3} =\dfrac{^{3)}3}{\ 1} \Rightarrow \dfrac{2x-1}{3} =\dfrac{9}{3} \Rightarrow .[/tex]
[tex]\Rightarrow 2x-1=9 \Rightarrow 2x=9+1\Rightarrow 2x = 10 \Rightarrow x = 5[/tex]