Resposta:

[tex]a) \: \: \frac{30}{3x} \times \frac{10}{5} = 10 \times = 150[/tex]

[tex] x = \frac{150}{10} = 15[/tex]

[tex]x = 15[/tex]

[tex]b) \: \: \frac{x - 6}{ x + 20} \times \frac{4}{2} = 4(x - 6) \: \: 2(x + 20)[/tex]

[tex]4x - 24 = 2x + 40[/tex]

[tex]4x - 2x = 24 + 40[/tex]

[tex]2x = 64[/tex]

[tex]x = \frac{64}{2} = 32[/tex]

[tex]x = 32[/tex]

[tex]C) \frac{x}{2} \times \frac{4}{x + 2} = x(x + 2) = 2 \times 4[/tex]

[tex]x {}^{2} + 2x = 8[/tex]

[tex]2x {}^{2} = 8[/tex]

[tex]x {}^{2} = \frac{8}{2} = 4[/tex]

[tex]x = \sqrt{4} = 2[/tex]

[tex]x = 2[/tex]