[tex]72-\{3a+\[[(2a:3+12):6+24]:3\}:2=13 \Rightarrow\\ \\ \Rightarrow\{3a+\[[(2a:3+12):6+24]:3\}:2=72-13 \Rightarrow\\ \\ \Rightarrow \{3a+\[[(2a:3+12):6+24]:3\}:2=59\Big|_{\cdot2} \Rightarrow\\ \\ \Rightarrow 3a+\[[(2a:3+12):6+24]:3=118 \Rightarrow\\ \\ \Rightarrow \[[(2a:3+12):6+24]:3=118-3a\Big|_{\cdot3} \Rightarrow \\ \\ \Rightarrow (2a:3+12):6+24=354-9a\Big|_{-24} \Rightarrow (2a:3+12):6=330-9a\Big|_{\cdot6} \Rightarrow[/tex]
[tex]\Rightarrow 2a:3+12=1980-54a \Big|_{-12}\Rightarrow 2a:3=1968-54a\Big|_{\cdot3} \Rightarrow \\ \\ \Rightarrow2a=5904-162a\Big|_{:2} \Rightarrow a=2952-81a\Big|_{+81a} \Rightarrow 82a=2952\Big|_{:82} \Rightarrow \\ \\ \Rightarrow a=36[/tex]
