Explicação passo-a-passo:
a)
[tex]x + 12 = 20 \\ \\ x = 20 - 12 \\ \\ x = 8[/tex]
b)
[tex]2x = 18 \\ \\ x = 18 \div 2 \\ \\ x = 9[/tex]
c)
[tex]3x + 5 = 11 \\ \\ 3x = 11 - 5 \\ \\ 3x = 6 \\ \\ x = 6 \div 3 \\ \\ x = 2[/tex]
d)
[tex]x - 1 = 35 \\ \\x = 35 + 1 \\ \\ x = 36[/tex]
e)
[tex] \frac{x - 9}{3} = \frac{27}{1} \\ \\ \frac{x - 9}{3} = \frac{3 \times 27}{3} \\ \\ \frac{x - 9}{3} = \frac{81}{3} \\ \\ \frac{x}{3} = \frac{81 + 9}{3} \\ \\ \frac{x}{3} = \frac{90}{3} \\ \\ \frac{x}{3} = 30 \\ \\ x = 30 \times 3 \\ \\ x = 90[/tex]
f)
[tex] \frac{x + 12}{5} = \frac{60}{1} \\ \\ \frac{x + 12}{5} = \frac{5 \times 60}{5} \\ \\ x + 12 = 300 \\ \\ x = 300 - 12 \\ \\ x = 288[/tex]
g)
[tex] \frac{x}{4} - 5 = - 1 \\ \\ \frac{x}{4} - \frac{4 \times 5}{4} = \frac{ 4 \times ( - 1)}{4} \\ \\ x - 20 = - 4 \\ \\ x = - 4 + 20 \\ \\ x = 16[/tex]
Espero ter ajudado!! ^^
