4. Решите уравнения: a) x + 9\(\frac{2}{9}\) = 15\(\frac{5}{9}\); б) 3x = 2\(\frac{2}{5}\); в) x : \(\frac{7}{20}\) = \(\frac{10}{21}\)

a) x + 9\(\frac{2}{9}\) = 15\(\frac{5}{9}\) x = 15\(\frac{5}{9}\) - 9\(\frac{2}{9}\) x = (15 - 9) + (\(\frac{5}{9}\) - \(\frac{2}{9}\)) x = 6 + \(\frac{3}{9}\) x = 6\(\frac{1}{3}\) b) 3x = 2\(\frac{2}{5}\) 3x = \(\frac{12}{5}\) x = \(\frac{12}{5}\) / 3 x = \(\frac{12}{5}\) * \(\frac{1}{3}\) x = \(\frac{4}{5}\) в) x : \(\frac{7}{20}\) = \(\frac{10}{21}\) x = \(\frac{10}{21}\) * \(\frac{7}{20}\) x = \(\frac{1}{3}\) * \(\frac{1}{2}\) x = \(\frac{1}{6}\)