Resposta :
[tex]\large\boxed{\begin{array}{l} \sf \: 3x + 20 = 50 \\ \\ \sf \: 3x = 50 - 20 \\ \\ \sf \: 3x = 30 \\ \\ \sf \: x = \dfrac{30}{3} \\ \\ \boxed{ \boxed{ \sf{x = 10}}} \leftarrow \textsf{Letra A}\end{array}}[/tex]
[tex]\large\boxed{\begin{array}{l} \sf \: 3x + 20 = 50 \\ \\ \sf \: 3x = 50 - 20 \\ \\ \sf \: 3x = 30 \\ \\ \sf \: x = \dfrac{30}{3} \\ \\ \boxed{ \boxed{ \sf{x = 10}}} \leftarrow \textsf{Letra A}\end{array}}[/tex]