Решите уравнение: 3x+(9x-1)/20=21-(3x+4)/5.

\[3x + \frac{9x - 1}{20} = 21 - \frac{3x + 4}{5}\ \ | \cdot 20\]

\[60x + 9x - 1 = 420 - 4(3x + 4)\]

\[69x - 1 = 420 - 12x - 16\]

\[81x = 405\]

\[x = 5.\]