$y_1 = 8 - \frac{1}{7}x_1 = 8 - \frac{1}{7} * 14 = 8 - 2 = 6$;
$y_2 = 8 - \frac{1}{7}x_2$
$0 = 8 - \frac{1}{7}x_2$
$\frac{1}{7}x_2 = 8$
$x_2 = 8 : \frac{1}{7}$
$x_2 = 8 * 7$
$x_2 = 56$;
$y_3 = 8 - \frac{1}{7}x_3 = 8 - \frac{1}{7} * (-1,4) = 8 - \frac{1}{7} * (-\frac{7}{5}) = 8 + \frac{1}{5} = 8\frac{1}{5} = 8,2$;
$y_4 = 8 - \frac{1}{7}x_4$
$9 = 8 - \frac{1}{7}x_4$
$\frac{1}{7}x_4 = 8 - 9$
$\frac{1}{7}x_4 = -1$
$x_4 = -1 : \frac{1}{7}$
$x_4 = -1 * 7$
$x_4 = -7$.