Решите уравнение : 17/21х+9/14=5/21 Даю 15 балов помогите пожалуйста

Решите задачу:

$\frac{17}{21} x + \frac{9}{14} = \frac{5}{21} \\ \frac{17}{21} x = \frac{5}{21} - \frac{9}{14} \\ \frac{17}{21} x = \frac{10 - 27}{42} \\ \frac{17}{21} x = - \frac{17}{42} \\ x = - \frac{17}{42} \div \frac{17}{21} \\ x = - \frac{1}{2} \\ ........................ \\ \\ \frac{17}{21} \times ( - \frac{1}{2} ) + \frac{9}{14 } = \frac{5}{21} \\ - \frac{17}{42} + \frac{9}{14} = \frac{5}{21} \\ \frac{5}{21} = \frac{5}{21}$