Explicación paso a paso:
[tex]4(3x + 1) = x = 3x + 20 \\ . \\ 4(3x + 1) = 3x + 20 \\ 12x +4 = 3x + 20\\ 9x = 16 \\ x = \frac{16}{9} \\ . \\ x = 3x + 20 \\ - 20 = 2x \\ - 10 = x[/tex]
