$\frac{6}{5x - 20} - \frac{x - 5}{x^2 - 8x + 16} = \frac{6}{5(x - 4)} - \frac{x - 5}{(x - 4)^2} = \frac{6(x - 4) - 5(x - 5)}{5(x - 4)^2} = \frac{6x - 24 - 5x + 25}{5(x - 4)^2} = \frac{x + 1}{5(x - 4)^2}$
при x = 5:
$\frac{x + 1}{5(x - 4)^2} = \frac{5 + 1}{5(5 - 4)^2} = \frac{6}{5 * 1^2} = \frac{6}{5} = 1\frac{1}{5}$

$\frac{2y - 1}{2y} - \frac{2y}{2y - 1} - \frac{1}{2y - 4y^2} = \frac{2y - 1}{2y} - \frac{2y}{2y - 1} + \frac{1}{4y^2 - 2y} = \frac{2y - 1}{2y} - \frac{2y}{2y - 1} + \frac{1}{2y(2y - 1)} = \frac{(2y - 1)^2 - 2y * 2y + 1}{2y(2y - 1)} = \frac{4y^2 - 4y + 1 - 4y^2 + 1}{2y(2y - 1)} = \frac{-4y + 2}{2y(2y - 1)} = \frac{-2(2y - 1)}{2y(2y - 1)} = -\frac{1}{y}$
при $y = -2\frac{3}{7}$:
$\frac{1}{y} = -\frac{1}{-2\frac{3}{7}} = -\frac{1}{-\frac{17}{7}} = \frac{7}{17}$