Tính

($$\begin{gathered} (3_2^1-2\mathrm{x}).3_3^1=7_3^1 \\ \frac{4}{9}.\mathrm{x}=\frac{9}{8}-0,25 \\ \frac{-\mathrm{x}}{21}=\frac{20}{7} \end{gathered}$$