[tex]\large\boxed{\begin{array}{l} \sf{Um\, n\acute{u}mero \rightarrow{n}} \\ \underline{ \sf{Dobro\,de\,um\, n\acute{u}mero \rightarrow{2n}}} \\ \sf{2n - 20 = 100} \\ \sf{2n = 100 + 20} \\ \sf{2n = 120} \\ \sf{n = \dfrac{120}{2} } \\ \huge\boxed{\boxed{\boxed{\boxed{\sf{n = 60}}}}}\end{array}}[/tex]
