Resposta :
[tex]10x + 20 = 40 \\ [/tex]
[tex]10x = 40 - 20 \\ [/tex]
[tex]10x = 30 \\ [/tex]
[tex]x = \frac{30}{10} \\ [/tex]
[tex]\boxed{\boxed{\boxed{x = 3}}} \\ [/tex]
[tex]10x + 20 = 40 \\ [/tex]
[tex]10x = 40 - 20 \\ [/tex]
[tex]10x = 30 \\ [/tex]
[tex]x = \frac{30}{10} \\ [/tex]
[tex]\boxed{\boxed{\boxed{x = 3}}} \\ [/tex]